351W starting problems

When you switched back to fresh water cooling did you change your thermostat also?
Fresh water engines ran at 140 before fuel injection came along while closed cooling systems ran higher temps, 180 maybe.

Your starting issue sounds like a new separate issue. Was there damage done when it overheated?

I would start with the basics since you know #1 is not sparking.   Verify your coil is getting power and then verify your points are set properly and in good shape.

Can you verify your battery grounds are clean and tight with not corroded.
Would need to check at the battery and at the other end of your cables.
The only way to verify a good connection is to remove, clean and reinstall. A little vasoline or dielectric grease will keep any corrosion from starting for the life of your battery. Just a thin film of the vasoline wiped over the battery terminal and the cable ends before connecting eliminates this problem. I have no idea why this actually works but it does. A mechanic told me to do this 35 years ago and many others have verified this trick to me. With a thin film it will look a little shiny but leave no mess to wipe off.

Starter having trouble turning the engine over after you had overheat issues, you might pull all 8 plugs and try to turn it over. You may find water sprays out of one or more holes.
That would be another issue to track down.
Starting issues when hot are sometimes tune up related, timing not set correctly.
It could also be the starter is just struggling to spin due to age or rust inside but that is normally true when cold and hot.

Your issue is a tough one, runs good then loses spark and the starter will not spin properly then you add in previous overheats to the equation.

I don't know of one simple answer that addresses all of those situations.
You are probably looking at multiple causes unless water got in cylinder #1, water fouled the spark plug and hydro locked the piston so it was compressing water not air and the starter could not turn it?    The thing that goes against this guess would be the fact it starts again when it cools off. If water is in a cylinder it stays there so you will not start hot or cold once water gets in.
Bad coils can work when cold and stop working when hot, this has happened to many people over the years.
I have seen starters work when cold but slow down when hot, I think they called this heat soak and some, even the factory fixed this issue with heat shields, saw this on Chevy V8 engines.

Slow hot cranking you describe is too much initial advance

If you click on the link and go to Topic 3 you'll have the DUI troubleshooting instructions for a no spark condition

The wire colors should be the same and the specs for the coil and magnetic pickup should all be the same or real close also. and the procedure is the same even though yours isn't a DUI version of the distributor.

Yours and the DUI are both copies of the original GM HEI .from the 70's

The modules are probably different internally but any GM HEI module with the same terminal arrangement will work in them to get you running again if you have a module problem, some perform better than others

link

MrMcD wrote: Maybe we could use the Terms: Closed System and Open System to describe the cooling options for clarity.

Then what would you call the raw water pump?

You would need to slightly lower the floats to avoid flooding due to the angle.

Wilhelm Hertzog wrote: MrMcD wrote: You would need to slightly lower the floats to avoid flooding due to the angle. Glad your making progress. Mark Will the angle not mean that the fuel level is higher against the front/primary metering block and lower against the rear/secondary metering block, so a slightly lower front float level and slightly higher rear float level than normal will be required?