What makes the 2v Cleveland heads "junk" and all 350M/400 engines "garbage" to you? The 4v 351C heads are huge and sluggish in most street driving situations.
Any 2v cleveland head ford made in the usa is open chamber. Open chamber heads are ripe for pre ignition and or detonation. Now Aussie 2v cleveland heads are closed chamber and all of the above goes away w/ the chamber "quench" (flat area). But thats just it,...there are no american ford closed chamber 2v "stock heads".
I agree 4v heads are pretty bad for the street "as is". But there are several companies making exhaust port restrictors to decrease some of the sluggish 4v street diveability issues. If you are a cleveland guy, I'm sure I don't have to tell you that.
The point being that open chamber 2v heads are undesirable over even big assed 4v ports.
351m and 400m engines aren't worth the time and money spent trying to improve them. The aftermarket abandoned those engines even while they were new. There may be AN intake, and a few "torque profile" cams made for those junkers, but the oiling system sucks, the heads are weak and they weigh too damn much. If I was gonna make room for a 400m, I'd bump it up and make room for a 460 instead.
I guess for a truck or a 4000 lb LTD they had a place. In a mustang????
Better off hotrodding a dumpster, because that's what a 351m and 400m is best at powering.