[tooski]

Also no one has said anything about the compression ratio, as that is not the subject of this thread. I will digress as that is known to happen on this site. From some of the info I have gleaned from this site, if your 389 is actually 10.5:1 compression ratio, a 068 may be too small for that CR and you would run into detonation difficulties, unless your UK gas has a higher octane rating. Pontiac rated their ratios about 0.5 points higher, so you may actually have 10:1. Only real way to know is to measure every thing: combustion chamber size, piston valve relief/dish, distance piston is down the hole, etc.