Compression ratio calculator?? And power figures?

If you're running a stock 318 bottom end, the pistons are probably .060"-.080" in the hole...and with just about any 360 head, your compression is probably gonna be closer to 8:1...but, just like you mentioned you need to know your head gasket thickness and diameter, how far in the hole the pistons are, combustion chamber volume, valve relief volume (if there are any).

...when you find your numbers, heres one I've used just to spitball numbers...

http://www.torinocobra.com/Randys_tools.htm

Hope this helps...

Edit: missed the part where you said milled to 61cc...my bad. I ran the numbers just real quick with what you provided, assuming .060 in the hole and an .040" gasket with a 4.060" bore...and it came up 9:1 just like you thought...