How do you know what type of pistons it has?

I am looking to buy an engine from a guy but he does not know what type of pistons it has in it. He had a shop build him the short block a couple of years ago and he does not remember what pistons they used. He told me it was either KB or Speed Pro. I can tell the difference from dish dome or flat but how can I tell what brand so I can figure out the compression height of the piston?