I have a 261 bored .60, shaved .20, ported/polished, stock cam, HEI, with 390 Holley, Clifford 6=8/Fentons, turbos. Ended up with 52s for primaries and bored 60s for secondaries and weaker than standard pump spring. Cooler plugs on back 2 cylinders and hotter plugs on front 4 cylinders.
Plugs burn even, starts well, runs like a scalded cat, mpg in mid teens with 3 spd OD. Took a bunch of trial and error this spring and summer to get it where it is.
