Tell him not only do they fit, but they fit with the stock 390 engine mounts. You just swap sides and turn them around. A buddy of mine has a '67 with a 429 in it, long tube headers and all. It's tight don't get me wrong, but the only clearance problem he's had is fan clearance, the 429 is longer than a 390. On another website www.fordmuscle.com, several guys have this setup.