I have a 1969 Camaro with a 396,bored .30 over to 402 cubes,forged pistons and crank,stock ported oval heads 2.19-1.88 valves,595 lift on intake and exhaust lift Competition cam,Edelbrock Torker 2 manifold,750 Holley double pumper,Msd 6AL ignition,4:11 rear end gears,28 inch tall tires in the back,150 horse power nitrous system,4 speed Muncie M-20 trans.The car runs great on 93 octane gas.I am not sure what the compression ratio is on the car but if i had to guess it would be 10.0.I know that the stock heads were the 360 horse power heads that chevy made and thats about all I know.The forged pistons may be 10.5.I want to keep a manual transmission and this car is driven only the street.I was looking into a transmission that has a overdrive like the T-56 or Tremec 5 Speeds so when cruising at 60 mph I would be driving at alot less RPM's.I have no idea what my gas mileage is because i have not had the car inspected for years but with my combination I would be lucky to get 10 Miles to a gallon??? Any one know what would be a good overdrive transmission that would fit without to many problems or mods???Also I would like to upgrade to Aluminum cylinder heads.I read about the newer Holley Oval Port Heads.They reduce compression almost 1 whole point and still make 51 horse power even with the drop in compression.I would like to get my compression down to keep out possible detonation although i have never had detonation before because i always put in 94 octane. I would like to lower compression a little so i can get 91 or even run 87 octane and still have the extra 50 Horse power.Anyone know who makes a similar or better cylinder head then the Holley Oval Ports that im talking about??? I believe the combustion chamber was 110cc for the Holley heads.