You need to check out some back issues of Muscle Mustangs & Fast Fords magazine regarding the 392. In the November 2000 issue they changed to AFR 185 heads and with no other changes got 537 hp at 5900 RPM and 505 lbs-ft torque at 4900 RPM. If you are going to change
oil pans you might think about getting the short block and adding the AFR heads yourself, etc. Look at the May 2003 and June 2003 issues for another 392 that produced 506 hp and 515 tq with a little milder cam. I'm with you, I afraid a hot 351 won't quite cut the mustard.