I would check the rotor phasing in the dist. the start retard might be causing a problem.

They are Daytona Boxes and distributors. It is also Carburated I had not mentioned that prior.

Worth checking

You rebuilt the starter that failed? I had one years and years ago that I had my starter rebuilt and it cracked the nose housing and left me stranded on a late October day. I ended up buying a new starter and never had the problem again. Being locked in at 32 degrees with a hi torque starter should not be a problem. And I have never heard of shimming one, just saying.

I meant the starters....

Because of that we are doing a new starter this time. We obviously will check all else again. Hopefully we will have the same luck you did.

were they piece of **** MSD starters like these sold by a lying scumbag company?

Nope the GM factory high torque

This one literally busted the nose off the aluminum housing, slightly bent both mounting bolts and took out the bendix. Still no obvious signs of a problem, plugs look great, no water, etc. Lost!

I think you might have a timing issue, loose wire, ground, tach or something. I had the same problem on my truck. Broke starter, cracked the side of the block where the starter bolt goes in. It appears that my crank sensor went out during the time I was cranking the engine over. Timing went funky and blew s#it up! lol.