I found a truck at the junkyard with a good set of heads on it, casting number 33417369. They have 'Hecho en Mexico' cast into the rocker valley. The only info that I can find is that they are 90-up GM Goodwrench crate heads, 76cc chambers, 1.94/1.6 valves. I also found that they are 'heavy castings'. Does anyone know much about these heads? Could they be ported and flow well on a 400?

are those the vortec heads?

CHP did a "Budget 350" series of articles that they started with that motor and those heads.

After milling 3 cc's off, using the Fel-Pro embossed steel shim .015" gasket, pocket porting, cutting the exh. valves with a 30* back cut, using the Comp Cams Xtreme Energy 268H cam, and running hooker 1 5/8" headers they were able to get 336 HP out of them.

IMHO, that's a lot of work for 336 HP.

http://www.chevyhiperformance.com/te...26/index4.html

These are low performance heads.

Don't expect great things out of them.

A 400 deserves a better head. Look into a entry level
Pro action cast iron head or a Dart iron eagle.

Better to save your money and invest in a better head.