[AcampoDave]

Looks like your heads are 416 (last three digits) 305 heads which are from the high output 305's. I use those on my 283 too and they breath pretty darn well on a 283. I hope they are in good shape because if so, they are a definite plus. Also, both 500 and 600 cfm Edlebrocks have the same "footprint". If one needs an adapter, the other would too. Post up a pick of your stock 4 barrel manifold so we can all be clear as to what you have on hand.