They actually made newer V-6's in the mid '70's. They were the 379 and the 432.

I super tuned my '66 GMC 1000 Pick-up with a 305 V-6 and got 15 MPG Hi-way. A lot of it also depends on how you drive them.

Bill


'60-'72 Chev/GMC Fan
GMC 9500 Fan
Detroit Diesel Fan