The problem is that the bigblock heads don't flow any more than the better smallblock heads. Backcutting the valves with no other changes won't do much. Heck, the MP templates don't do that much, still won't get an iron head within the aluminum head out of the box.

Find Steve Dulcich's three-part article on porting B/RB heads. The link in the last post is the first of the three parts in Dulcich's bigblock head trilogy.
Be sure to also find and read Fast68's writeup on porting 906s, which is in the Tech archives.

Bottom line for me is that the 40+-year-old iron (they were never steel) heads flow poorly and have a lousy combustion chamber, except for the 915s. Any of them will cost more to port and rebuild than a Stealth or other entry level aluminum head. After they are ported, the iron heads have been known to crack and then all that money is up in smoke. Don't do it.

R.