Manual trans run it at 800 rpm. It's fine. This is NOT a factory cam with 200* of duration, it's in the mid high 220's and needs more RPM to run right. Additionally, run it lower and the splash to oil the cam is minimized at idle which is BAD!

Turn the mix screws to about 3/4-1 turn out.

Lose transfer slot? If the mix screws don't do anything, it's likely dropping fuel in from somewhere else (ruptured PV diaphram) or dripping boosters is likely. At least you don't have the in gear issue that an auto trans would have. If need be open the secondaries slightly. Use a .015 feeler gauge or some paper layered up between the set screw and arm on pass side to hold it open as a test.

The inside of the carb looks black which usually means it's really rich with inadequate initial timing. Now that the timing is about right, the rich side needs to be solved.