Where do they mark the heads on a big block ? So I can figure out which heads are on my 440. Plus are the 906 the best flow ones of the cast iron heads with a 10to 1 compresion ratio?

Usually on top the head under the valve cover
http://wwnboa.org/mhi.htm

I always like the 906 but the 452's have hardened seats and so on.

Aluminum heads are a better deal in the long run with the cost of proper rebuilds taken into account!

Numbers are cast on top of the head, underneath the valve covers. IIRC, there may also be a number on the underside of the head, cast into a small recessed area. You are interested in the last three digits, for example 906, 452, 516, etc.

Although the 906 heads are known to flow pretty well, the "best" heads are probably the 915s. These would have similar flow to the 906s but are closed chamber so you can get better compression and can also get quench.