Jeff, there is a flat section on the passenger side front of motor where block meets head. There is a number with suffix letters stamped on it. Wire brush that pad and post the numbers and letters. Read the pad carefully with a good light at different angles. This is how you tell what the motor/block is. Other parts can be added over the years and their casting numbers can corroborate the "Serial no." or prove parts are replacement.
Best place to rebuild that carb is at your house. Buy a kit, take carb apart while taking pics and writing down thoughts. Keep track of parts removed, clean the reusable parts in carb cleaner. Put it back together carefully and set float per instruction. There are Youtube's for this carb as well as text online.
We all had a first carb rebuild. As long as you are clean, careful, search and are motivated you will do fine. Kits are $25, gal of cleaner $20.
