L31 heads from a boneyard, casting # 12558062 or 10239906. Magnflux 'em for cracks. Fit new STOCK
springs and seals. Make certain seals are fully seated on the guide boss by tapping them with a socket and small hammer. The stock springs will work well with the mild cam and will not pull the rocker studs out of the heads. Doesn't matter whether the heads have hard inserts in the exhaust or induction hardened seats, either way will work. Same casting, both styles flow the same. Give 'em a good valve job and otherwise leave 'em alone. Use the rail rockers that came on the heads stock.
Align-hone the main bearing bores in the block and cut the block decks for 9.015" block deck height, referenced off the main bearing bore so that you know the block deck height is equal on all four corners. This will insure that the heads sit level and flat on the deck and that the intake manifold will sit square to the heads with no gaps to cause an internal or external vacuum leak. Use GM head gasket #10105117. Static compression ratio will be 9.1:1 and squish will be 0.042". Use Edelbrock #7116 Performer RPM intake manifold. 600 carb is all you'll need.
Makes 365 hp @ 5000 rpm's with a double torque peak of 420 ft/lbs @3500 and 4000. Should make this power on crummy cat-pea pump gas without detonation.
Cam begins making power at 1200, so it's your call whether or not you need a looser converter. If I did anything at all with this combo, it would be a mild 2000 stall unit just so I didn't have to contend with the car creeping at stoplights.