Cliff: Here is an interesting article on the swap-out of different sized Dart heads on a 363 bottom end..I'm just offering this for the entertainment value and perhaps you may glean something from reading the comparison.
Cylinder Head Comparison Test - Muscle Mustangs & Fast Fords Magazine
...and to Brent's point...there are other options out there, I'm just working with what was on my engine....another comparison:
Cylinder Head Guide For Your Street Stang - Heads Of The Class - 5.0 Mustang & Super Fords Magazine
When my 347 was on the dyno, it produced 430hp/420tq at the flywheel with 44IDF's. It also ran 12.4 and 105mph trap in the quarter. With the same Dart Pro1 heads, same cam save for the lobe separation, and 48IDA's, the car ran 11.9s and 115mph trap. Simple on-line calculators will tell you that's 50hp, but the car hasn't seen a dyno since I've moved to the IDA's.
- Allen.