Going off your Head cc, 498.5 engine cc, using a 82.5mm x 1mm H/G, std 4wd pistons,
4mm of piston skirt, and 3mm off block,
i worked out roughly 10.97:1.

or if you take 3.3mm off pistons, and 3mm off head = 11.38:1 c/r.


but you will still need to cc check it when you do it,