It's a temptation on forums like this to try to troubleshoot by tossing out every guess you can come up with. Unfortunately that sort of procedure doesn't work very well in the real world where tools meet tasks. Troubleshooting is a matter of elimination; you start with the combustion tripod (ignition, compression, fuel) and test for sources of grief.
OP, you've tested compression and you know that it's healthy. You've tested ignition timing and you know the ignition is timed correctly and advances as it should. You've inspected cam timing by observing the position of the pin holes in the camshaft, so you know timing of the OE camshaft is correct. You've found a charging system defect and corrected it.You found a crankcase breather defect and corrected it. So far, so good!
Now there's a little principle that we forget too often, which is that some electrical problems show up only under load.So the next thing you might check is every connector in the TCI system that the liars at your shop ("Didn't know there was a problem, didn't test it above 3K, your gearing is too high," etc.) may have pulled apart. While you're testing, with the key and kill switches on, compare battery voltage to voltage on the 12V line into your ignition. If there's more than a 0.5V difference, clean switches and connectors.
Did the shop monkey with your carburetors? Maybe not, maybe so. You might want to have a look at the slide diaphragms.
My bet is on ignition defect. Good luck to you.