thanks for your input snoopy i think ill go with a 84 bore but i do have 2 questions

a. how high will my RPMs get with the different lengths in the finial drive?
and
b. 91 octane would be the highest i prefer so i should stick with 12.5 based on this or what am i looking at here?

i guess i dont fully understand why the octane makes that much of a difference.