400 engine Help Needed

The truth is, the 8.5 to 1 is the factory rating. If checked, you are really probably in the 7's. Not busting on you, just letting you know I haven't ever seen a non blueprinted engine of any brand make it's advertised compression.
You can only do so much with the existing pistons. If you are willing to pull the engine, an aggressive block deck, and some milled closed chamber heads would be your best bet, along with the .020" shim head gaskets.

For the cam, I'd keep duration on the short side, in the 220ish range at .050", given it is in a heavy car. I really like the Performer RPM for an intake. Good luck.