mid to low 16's with stock equipment, including the 2.80 gears, were normal times for 65-66 mustang V8's. the hipo's ran quicker, usually in the mid to low 15's. as for the heads, there were a couple of differences between the "standard" and the "hipo" 289 heads. one was the screw in studs, the other was the cast in spring seat. other than that there was NO difference between the heads.