I have a set of pistons very similar to those, and the dome volume is more like 28cc...but again, it's hard to be accurate looking at a picture. It's always hard to figure what you're trying to do if you're not pulling a head to measure a chamber volume. I have seen the published cc's of stock heads to be way off, 10cc's or more in some cases. This will change your C/R quite a bit. But I know what you're trying to do, and I guess being conservative is a better way to do it. Does your friend have the spec sheet or number on those pistons?? That would tell you the exact volume. I have a fair knowledge of big blocks, not an expert by any means, but based on what I have seen in the past, if your chamber volume is about 105cc, I'll bet your c/r is all of 9.3/1, probably closer to 10/1....The deck height will also change that quite a bit, as will the gasket bore...they both add lots of cc's. But it sounds like a great combo so far, have fun with it. Be careful with your cam choice, remember, smaller duration = low end torque, at the expense of high end horsepower....but unless your're racing it, you want your power at lower RPM's...if you want a really lumpy idle, look for a cam ground on a 108 LSA vs. 110 or 112....but if you do that, you'll lose a little vacuum...it's all a trade off, so shop carefully. Talk to a cam grinder if you can, like I suggested above. John