Thinking of building a 470 with parts I have in a 400 block parts I have is 400 block 3.9 stroke crank 440-1c heads a set of 4.375 pistons with 1.295 ch these pistons are out of a 440 engine with 440-1 heads. I want to buy a 6.7 length rod.With those parts here are my 2 questions 1. Will the pistons work in the 400 if I bore block to 4.375 2. How much can you safely take off the deck of the 400 since this combo will leave piston 035 in the cylinder

You can get an 0.027 head gasket from Cometic so if you shaved a little bit off the deck you could end up with an 0.045 quench which wouldn't be too bad. Depends what type of compression ratio you're looking for. If the CR isn't correct you might be better off selling those pistons and buying the correct ones for your build.