Drilling through the two rings:

Using the nonpowered drill press to keep the tap perpendicular

The two rings finally screwed together.   the original Canon ring will be epoxied to the lens body

The new "key"  to keep the inner guts from rotating.  I took an original piece,  and squeezed it flat.  Located it carefully,  and drilled two holes for a "slip"  fit of two original screws.  All these screws do is pin the piece in place while the epoxy dries.  I have no taps this small

The major pieces.  The entire lens can be dissasembled my merely unscrewing the focus.   I BELIEVE   the focus helix's  are triple, not "quad."  This means that the threads  "start"  every 1/3 turn,  allowing some tuning on the depth of the focus elements  "back" into the body.  I spent about an hour playing with this "feature"  in order to get the original index marks to line up

The lens is now complete and "ready to go"  except for epoxying the rear adapter/ring onto the lens body.   Before I do that,  I want to get out in the light and be SURE  we have infinity.  Because this is a short lens (28mm)  and the DOF is so deep, it's really hard to tell.  I'd kinda like to have some "back focus"  to  "make sure."     Anyway,   what we have done so far will allow me to install the ring on the camera,  and hold the rest  up against  in it's final position.   With any luck, it'll be done tomorrow.

Been raining and snowing here,  so it's hard to get out and do much.  Foggy and hazy part of the time,  difficult to find good, clear, distant targets

First,  no modification to the inner lens group is necessary,  except to cut off the aperture lever in the rear.   The entire inner lens group comes out by removing one nut/retainer on the rear.

I thought this over for about a day. 

THIS CAN BE PERFORMED WITH NO LATHE.   Only files, or a Dremel type grinder,   a couple of small screwdrivers,  and normal hand tools are needed.

I haven't   decided whether to drill and tap the parts for assembly,  whether to solder  the adapter to the body ring,  epoxy,  etc.

I used a Nikon-to-Canon  import adapter,  which is brass,  and is two piece.  I removed the front piece,  and will only use the rear as a mount,  which makes it thinner.

Here's  the pieces out of the lens which will be used.  The upper left is the "inner lens group, which is held in place by the nut  just behind.  The screwdriver is pointing to a hole in the black section from which a screw  is removed.  This "keyed"  the lens group to hold it from rotating,  but will not be used.  The inner group  will not index  at the original rotation.  Left center is the "inner body"  which  holds the lens group, and is unmodified.  Left lower is the focus control ring,  screwed to the focus helix.  Lower center is the main body.   Lower right is the original Canon retainer, which will be used as part of the mount.  Center right is the rear  section of the Nikon-to Canon adapter  The little brass piece   is originally a stop for the focus mechanism.   It turns out that it sticks out enough  next to the aperture mechanism  in front,  that it interferes with allowing the lens group to screw  "back"  far enough,   and simply will not be used.:

First step is to remove the  bayonet lugs  from the original ring--the one you operate to install/remove the lens from the camera.  Again, you could file or grind this.  Remove the bayonet lugs,  out to the "major"  ID of the ring:

Next  is to cut the shoulder to a  larger  ID  on the rear of the body,  so the lens group can come back further for infinity.   Again,  you can do this with files or a grinder:

Here's a picture  with the inner section  stuck into the main outer body ring BACKWARDS,  just to show how we now have clearance:

Below illustrates  the focus helix, removed from the outer control ring.   Originally  Canon used round head screws,  which interfered with allowing the inner section to screw back in far enough for infinity.  I simply  countersunk the original holes,   and used flathead screws.  THESE SCREWS  came from the dissasembly of the Nikon adapter,  which is two-piece.

Also,  to gain just a little more,  I discovered the focus threads  are a double thread,  that is, you can start the helix in the body  in either of two places  180deg apart.  By re-installing the outer focus control ring  in the "wrong"  spot,  and playing with this thread,  I gained another tiny amount "back"  into the body  for infinity  Below shows the focus control ring re-installed on the helix,  with the countersunk screws--which originally came on the Nikon adapter.

Here are the modified pieces,  getting closer.  Top left is a "first"  Nikon-to-Canon adapter,  which I ruined.  I was trying to turn off the two  ridges on the face, which may not even be necessary.   To the right is the "second"  Nikon adapter, rear section.  To the right yet is the Canon retainer, after removing the bayonet lugs.  Top far right is the inner lens group.

Lower left is the main body,  to it's right is the modified focus ring,  and right further is the retaining nut for the lens group.  The washer  will NOT be used as it adds yet another tiny bit of "back"   distance for infinity.  To the far right is the inner body, unmodified

Below shows how the modified retainer ring will fit onto the body.  I may just epoxy this,  as the two have threads and other ledges which  will "catch"   I also may get some screws and a tap and screw it together

Here's how the mount,  the retainer,  and the lens body would fit.   I might solder or screw the mount to the retainer,  and then epoxy the retainer to the body.  The two just happened to be the right size  to fit

Once that's all done,  assembly should progress easily.  Install the focus ring,  and screw all the way in,  then back out to the inf.  mark.  Screw in the inner housing,  and then install the lens group.   The "play"  here is,  that you must  screw it in as far as can be,  without binding the aperture control ring on the front.  This becomes your maximum  "back"  position.   At that point,  I'd have to install an index screw(s)  to hold the inner group from turning as you focus.  Finally,   loosen the inner lens group  (rear)  retainer nut,  and rotate so the aperture markings are   "up."

Tomorrow,  I'll try and check for inf.  focus,  and see if I can drum up some no "0"  or no. "1"  machine screws and a tap.