On my 70 with a 351w I am running hooker competions headers. I have had 3 different transmissions in there. With the fmx they fit perfect. With the 4 speed I had to rework my z bar and still put a couple "clearance" dents in the tubes. With the AOD the collector flanges are right up against the flange on the pan, even after I massaged them a little but not enough to cause a problem.
John