I’ve never tried building a 650hp SBM, but it seems like attempting it with heads that have a std port opening and a std pushrod pinch, along with small tube headers is asking for a lot out of those parts.
I’ve done that and more, but it’s not cheap or easy. As I’ve posted before, I certainly did it the hard way, but either way you try and get anywhere near 2 HP/CID it’s going to cost big bucks no matter what name is on the valve cover.