I figured you'd thought of most of this.... but just the whole sound of that cam makes me really suspicious. Again, I have laughably little experience rebuilding engines, but you get a cam from a supplier with lower prices, it looks funny and the measurements aren't right, and you keep having problems that could be cam-related. It just seems like a really plausible tale.
But, the 261C cam has several pads that are off the lobe between .108” to .112”, and I posted photos of this...Even though Tod at engbldr said it's OK, I still don’t think the alignment should be off that much
If I read that right the new cam is at least .04" smaller than the old, and considerably more in places. I'm not an award-winning racecar tweaker, but speaking as a machinist, If I'd made any part, let alone an engine cam, that far off it would've gone right to the scrap bin. I literally can't remember the last time I held a tolerance that loose on anything! Of course, I've never made an engine cam, so my knowledge is limited. But the idea of such loose tolerances being "OK" gives my inner machinist fits.
This is just an under-educated opinion. It is subject to instant revision as more knowledgeable say what they think.