Definitely fix the fuel gauge problem.
The correct "single R" (assuming one-barrel Rochester B) carburetor for a 261 is hard to find. If your carburetor is for a 235 engine, it may run rich.
Tuning for maximum vacuum is a shortcut method to getting the engine to run. I would tune-up with dwell meter and timing light.

"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."