You need to know all the dimensions to figure the actual compression. Regardless of your final compression number, you really want to make sure it's calculated, not assumed.
Exactly. Those pistons may be rated at 10.5 to 1 but they will only give you 10.5 to 1 compression if they are a certain height in the deck and the head chamber volume is at a certain volume. You need to check these things before you do anything else or your just guessing and may end up with 9 to 1 or 12 to 1 compression ratio.