Why not just buy a pair of pillow blocks and appropriate diameter stub shaft then to form a jackshaft setup? Weld on your sprocket carrier. Far easier to fab a mount setup for it too since the pillow blocks will be setup for such a fashion.
Cheap pillow blocks:
HCAK200 Series - theBigBearingStore
You can buy shaft stock on their as well but you can find it non-keyed and cheaper elsewhere, like a go kart website.
Just a thought for you instead of buying an ATV setup. It’s essentiall the same idea behind the primary drive for snomobiles, they just used flanged bearings instead of pillow blocks. It’s not weight loaded on your jerry rig there, so it doesn’t requires the taper bearings. Just radials and maybe a lock collar to set a tiny freeplay.
Tis how I did it on that one I made years back for a guy
.
Yea thats pretty much what I am looking at now. It will make any adjustments needed a lot easier. Thanks for that site! I plan to go with flanged bearings though, it would be easier to setup the brackets since I plan to use the stock trans mounts.