Hi Terry, The jaqckshaft is just a piece of 1018 cold rolled steel I got from a machinist friend. I used the stamped steel 3/4" pillow bearings to save weight over the cast iron ones. They have setscrews to lock them to the shaft.
You can buy keyed shafting from the go-cart vendors . My shaft wasn't keyed, so I drill a 5/16" hole about 1/4" deep to accept allen head bolts in place of the 5/16 setscrews, to lock the pullies in place.
I made my roller by turning down a 3.5" steel pully to fit tightly inside a short piece of thickwall 3.5" pipe. I had to use 1" square tubing spacers with the pillow blocks to make the large dia roller clear the mount when installed. There are some high clearance pedistal type pillow blocks on e-bay that would eliminate the spacers.
Spotwelded the pully to the pipe sleeve inside, and chucked it in the lathe on the jackshaft for a manderel. Turned it true and knurled it. 500 miles on this build now,no noticable wear or problems yet.
This has turned out to be a very reliable,efficent and simple drive train,lil more complicated now with 2 speeds though.