Need help with rebuild

Not really a "slant six issue". Sounds like a general "any gas engine" issue, so shouldn't stump the guy.

Check for a strong spark using an in-line spark tester. Harbor Freight has a real cheap one that works OK. With spark and good compression (you did check?), it should run on starter fluid. Just keep spraying shots down the carb. I did that long ago for a girl w/ a VW Jetta w/ Bosch Jetronic (not a slant!). Ran fine as long as I kept squirting starter fluid, and she didn't see understand why she couldn't drive home like that (with me under the hood?). Her fuel pump had failed.

What carburetor do you have? We know all about them here. The choke needs to be tightly closed when cranking, then pop open slightly by the "choke pull-off" or "unloader" so it doesn't die rich. Those often have a torn diaphragm.