when I rebuilt mine I did a stock rebuild kit and I upgraded to the better bearings, biggest comp cam I could find for computer controlled, new valve springs flat top pistons, summit shorty headers, a few odds and ends and I bought a head from a boss for 75 because I had a few cracks in one. I did not know how to do a rebuild or the tools so I paid the boss 500 to help me through it. all in all I was in it about 22-2300 bucks.
I wanted to go vortec heads and bore .30 over but the cheapest used heads i could find were 35o a set and I wish i would have gone .30 over but budget did not make this possible... wish i would have went for it anyway and figured something out
P.S. i dont get anywhere close to 2o mpg though.... about half.. around 12 in town maybe 15 highway with a good tail wind lol