Originally Posted by lo_jack

If you have a MIG....

M50/M52 manifolds bolt to an M54 head, provided you use manifolds with a single flange, and they do not drop straight down from the head off cylinder 1 and collide with the A/C compressor. People have put earlier engine headers on E53, but the problem is clearance, as you already know, not really the flange. The thing about the flange is there are not studs/bolts in every hole on the E53 M54 head, so to get enough clamping, it is said, you have to use a single flange design and use all the fasters available.