just watched the same video and interesting that the early 8-1/4 used a similar crush sleeve to the 8-3/4 --- someone on here must have access to early service manuals and could chime in with the year that first shows the smaller late model crush sleeve.
before you buy the solid spacer , i would measure the crush sleeve you took out to see how it compares size wise to the crush sleeve for the 489 case --- if close on length ( which is 3.00 inches ) and other dimensions ,, i see no reason why you could not use it in your rebuild.
if you can't find an original longer crush sleeve ,,,another option you have is the stack a .020 shim on top of the old crush sleeve this would give you some free play and be able to crush the sleeve to the pinion preload needed.
