Contact Victor Machinery Co. about a milling machine arbor spacer with a 1 1/4" inside diameter. Same size as a GMC crankshaft snout. It will be a snug slip fit on the crankshaft and the OD should be about right. If it's a little too big, a belt sander will take it down to an acceptable fit since it won't be running against the timing cover seal. They come in all sorts of thicknesses so you can adjust the position of the damper, and they already have a keyway broached into the inside diameter. Measure the difference in the snout length, and purchase one or more spacers to get the proper position for the belt sheaves.

https://www.victornet.com/detail/SPA-1-1/4-1/2.html

Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!