350 vs 366 performance?

[MARKDTN]

366 has the same crank as a 396 and 427. It is steel and some of the best material made. But a 366 has a tiny bore, awful heads, and is a tall-deck to boot. Take the crank out and sell the rest for scrap. The intake, even though for a Holley, only fits a tall deck-and the Holley carb has a governor in it. The distributor is longer, the exhaust manifolds and accessories don't fit anything but a school bus or big truck, etc. Very little demand in my experience.

The 350 is better, but still old school 2-pc rear seal. I would use it. If you don't mind building something and doing a bit of horse trading; then pull the crank from the 366, sell the 350 running, buy a 454 with a bad crank, build a 427. Now you got power and torque.

Or sell both and/or parts and go buy something fuel injected that is wrecked and do a fuel injected swap. Camaro/Firebird (or Corvette) for Tuned-Port or LT1, Caprice for LT1, 96-99 truck for Vortec. That stuff is out there.