I'm in the middle of a similar project right now, and although you want to avoid removing major components I gotta say that there are a lot of reasons to consider removing them. The following items can be removed without a huge hassle if you have basic tools:
- Distributor & plugs
- Generator/alternator
- Manifold and carb assembly
- Upper radiator hose
- Lower radiator hoses and water pipe
- Timing cover & inspection cover (optional)
- Starter (simple to remove but awkwardly heavy)
- Oil return pipe
- Valve cover
If you remove these parts, you can:
- Inspect them and the components under them
- Clean and paint them off the engine
- Strip and paint the engine much more easily without so many obstacles in the way
It's more assembly work but I think it would improve the repainting results. For example, you could take the manifold to be bead-blasted and then paint the intake with engine paint and the exhaust with high-temp paint. That's going to be practically impossible to do without removing it if you want durable results.