Rough Running

I have a 1971 daily driver and it is reasonably stock with unknown miles.

I run:

Mallory Dual Point mechanical dist

MSA Header

NGK Plugs and wires

MSD Coil

It runs strong but I am having a problem suddenly and am stumped. It “rumbles” when the car runs and seems to lack power a bit. Normally acceleration is nice and smooth but it idles rough and “growls” when I get on the gas. Almost like its missing but not quite.

I have replaced plugs, timed it, adjusted/synched carbs (SU’s), replaced wires and swapped coil. Each thing helped a little but the problem persists.