My (74) fire wall is very, slightly different. How tight was it? I wonder if going with the 6.4 if you can keep from modifying or if there is just simply no way around it. I have a 5.7 but have strongly considering selling it and going up to a 6.4. But, if there are a bunch of heavy mods that have to go into it, I may just stay with a heavily modified 5.7 instead. The allure of the 392 is almost too much for me to resist, but I don’t know if I’m interested in cutting on the fire wall. But, then again, I highly doubt anyone would ever know. Not like you can see it....