If you want stump pulling torque for a heavy vehicle, go with a head in the 170-185cc intake runners. If you're looking for upper rpm hp, some 190-200cc runner heads are the choice. Vortecs do make a super torquey 383 but they are pretty much done at 5500-6k rpm which is good for a street car. The difference will be like night and day over the heads you have. Go with 64cc chambers and adjust the quish as Tech advised and you won't have problems.