My other thought is to use a round, tapered punch to expand the last spiral so it is larger than the hole in the upper stop.  That seems simpler...

A course thread nut, cut in half and used in a vice as a clamp around the spiral might work as a keeper without distorting the spiral too much while knocking in a punch and expanding the end turns?

Just an idea...

Continuing to install my hand grip controls.  Got the outer spiral cables mounted and cut to length, and the cable end sleeves installed on the mag and carb.  When I installed the new spirals and inner cables, there was a point where the left grip would hang up and refuse to move.  If I gave the inner cable a push, it would free up.  Definitely not smooth enough to use.

Researching the R&O Manual, this board, and my collection of paper WOWs, I ran across the attached diagram in Volume 6 Issue 2 from March 1989.  It's a dimensioned drawing of the spiral block pin, but importantly to me, it describes the areas of wear.  When I looked at the old pins I was trying to re-use, it became obvious that there was significant wear and a definite shoulder,  and I suspect that was binding up when the old pins were installed in new spirals.   I've got new blocks and pins on order.   This diagram did not get included in the R&O Manual.

Passing this lesson learned along in case anybody else runs into the issue.

Wow, Carl-Erik - those are some rough looking parts.  Amazing what we think is usable.

I've attached a photo of my hand control block and pin.  The wear from the spiral is clearly visible.  

My '29 came with a '31 handlebar and a mis-matched set of spirals.  I replaced the bar and spirals, but tried to re-use the blocks and pins.  Should have figured that wouldn't work...