I'm getting ready to put a 496 together out of an old gen 4 tall deck block with an 871 15 over blower. I'm going to run 8 to 1 compression. I have 2 sets of heads, one set of 990's and also a set of 188's. The 188's look to have bigger intake ports and the valves are a little bigger. Also I have a solid roller cam that I think is an Isky don't know for sure. The #'s on the ends read, 19536, 97J1A with a sideways D and on the front it reads 112 BGK. Any info would be great. This is going into a 20 Spectra, looking to spin it around 5800 to 6000 RPM's.