I would use a 400 block as their physically smaller. larger bore than a 440.the webbing in the 230 block is like an aftermarket block while the 630 block should suffice. the 440 block is good for around 600 hp or so but has a much weaker webbing than a 72 to 74 400 which in my view necessitates a girdle as the 440 block is quite tall and has a tendancy to crack the main journal webbing.The 400s also make great strokers and will flat out smoke a 440 due to lighter internal weight, hope this helps,happy holidays all.