[Rockdriller]

I am a bit turned around after this read.....I used to have a clue.....an' now I'm wondering if [I] do but maybe I don't.
Is it possible you mean the input shaft when yer saying tailshaft...?

Also....for the record....FYI....
When working with the needle brgs in the main shaft...if you clean everything up with brake cleaner or hot solvent....you can wipe some assembly grease or even brg. grease on the shaft and then stick the needle bearings to it. They'll stay right there while you put things together...and won't give you any trouble.
The flip side to that is to grease the other side (female side ) of the shaft and stick the needles in there....and then assemble...

Good luck,....