Hi Birge;
Sounds like you've tried all the usual culprits. I'm wondering about your plug gap though, "gapped heavy for a fat spark" could be your problem if it's too wide. I'd go back to original settings and try it. Also, when you get your new dizzy, after setting the timing initially with a light, I'd advance it until you just begin to hear a "ping" under heavy load. Each engine seems to have it's own sweet spot on this. My '54 235 now has about 10-12 degrees initial advance with vacuum advance disconnected, and checked at idle with a light.
We've been to your fair city, we ate a couple of times at a BIG cafeteria style restaurant. Excellent!
Good luck with your 'bolt.
