How to achieve a desired compression ratio?

[Howieau]

Ok its time to order my pistons, Ive completely changed my mind on the whole comp ratio setup and am going to go for something between 8.0:1 and 8.4:1. I found these puppies that I might get but before I do I need to figure out the math;
http://www.pistons-online.com/sport....a&st=43&end=43

Based on your post info oldcorollas, this is what Ive come up with, tell me if Im wrong.

Swept volume with 86mm stroke and 87mm bore = 511cc
Stock 0.8 headgasket at 87mm was 4.75cc (so to find what the capacity of a 1.42mm head gasket thats mentioned was used on that website, I did 4.75 / 0.8, then multiplied the answer by 1.42) = 8.43125cc
Combustion chamber = 49cc in head (which I read is for stock gen2 3sgtes) + 13cc (stated on website for piston dish) = 62cc

511 + 62 + 8.43 / ( 62 + 8.43 ) = 581.43 / 70.43
Equals 8.26:1 which would be ideal.
Now that im not going with 9:1 it doesnt have to be so accurate, just as long as it lies between 8:1 and 8.4:1. Please let me know if I've done this right. Many thanks!