That is exactly the issue I found with the 340/5 in the sled the wife rides. Years ago, I bolted a starter on it, only to find that the starter wouldn't turn the flywheel. I think the early ring gears have three more teeth.To be clear the ring gear on the /5 motor had more teeth , was larger diameter than the /23 ring gear I wasn't expecting that. Wade
The change was made with the /21 on up. The early engines have the starter motor studs on an angle, which makes the bottom bolt a PITA to get to. The later engines have the studs one above the other, which changed the location, which required the change in ring gear diameter.
On the issue of clutch alignment: section 50, page 25-2 in SM 2100, shows how to use the tool.
On page 40-1, it gives the Drive Sheave Parallel Offset: Salsbury - .250" Comet - .300"