I agree with Thunderbucket plus a .30 over bore will help. Lighten and balance the crank. If you want to stick w a 6cyl, then just take that enging out and put in a mid 60's 250 straight 6 from a truck and follow the ideas posted . The 250 is stock with 155hp , plenty of torque, and can be built up to put out well over 200hp.