Ok I have found a long block that the person that rebuilt it has used 351w heads and had the machine shop rework the heads to use GT40 valves. What would this gain over using GT40 heads or would it be gaining anything at all?
If they are 194 valves it would be an improvement. but not all the info is there to guess. I am guessing on the valves that are in it.
If they went that far to do heads up like your saying, there probably redone somewhere else.
Which 351 heads are you talking about? '87 and newer 351's used the same E7TE heads that HO Mustangs used. A larger valve opening might help a bit, but probably not much without some serious porting to open up the ports...