I have had several holleys new out of the box that the float was bad and making the float level way to high, causing a rich condition. Changed floats and all good.

 

That was always my problem with the 1850 I had on the 302. It would never stay running the same two days in a row, and would constantly blow through power valves. That was just before the dawn of the "blow-proof" valves if I remember. After trying one of those and ending up a week later with the same symptoms as a blown one, but being told that couldn't be it, and changing it out to a new one fixed it, I wasn't too convinced of just how "proof" they were.

Ditto what was said about engines sitting.

Another thing that can create, or at least encourage white smoke out the pipes is improper timing. When I would retard mine I would get smoke/steam. When I would advance it too much, I would get the same smoke. But by too much I'm saying by a LOT. As in 18 to 20 degrees BTDC.
Too much for it to run happy, but I was experimenting and noticed the smoke.

The initial previous bogging down sounds like a slightly lean condition. The increased symptoms after adding a large, free-breathing exhaust just bears that out. You almost always had to re-jet a carburetor after adding headers and dual exhaust. The increased bogging when going to a leaner jet sounds like it's leading to the same conclusion.
Although when you went to the richer jets and it didn't cure it, maybe by that time you were also dealing with the bad power valve and not enough squirter.
So try the larger squirt of accelerator pump (verify in the venturi that the squirters are both putting out healthy bursts), and advance the timing a bit even if you can't find a pointer and marks. Then while it's idling check for vacuum leaks. Also check, clean, or just replace the PCV valve.
What about rubber hoses on stuff? Rubber caps on unused ports? These things deteriorate a lot faster than they ever used to, so get to checking for vacuum leaks for sure.

Good luck.

Paul