The 4.3 core we bought for 50 bucks had a 2500 stall converter bolted to it and some 1.625" OD shorty headers that should fit anything.
Contrary to opopular opinion, I like shorties as opposed to long headers.
Why? Because they are not rpm sensitive. They will not do anything stellar at any particular rpm range, but in turn they will not cause any bad effects in between.
If you reduce primary pipe length, say cut in in half, there will be twice as many pressure pulses. Both good ones, low pressure, and bad ones, high pressure. BUT; Those pulses will be half the strength that the long header produced.
Gearhead, your right about the 1.6 intake rocker not helping unless the exhaust side is improved in kind. That is why the 1.6 exhaust valve and 6 degree added exhaust duration on the cam at .050".
Advancing the cam helps the intake breathing, but hurts the exhaust scavanging cycle during overlap.
Quite often people see no improvment when they increase intake rocker ratio until they take out the cam advance, helping the exhaust.
Look at it this way. Increasing the intake rocker ratio lifts the intake valve faster making the engine think the cam is advanced more.
The split overlap position ends up more towards BTDC, or advanced.
Too much advance= no HP, just torque.