I'm not familiar with cam and head upgrades, though I'm curious as to your 'whimpy' comment on the 4.6L 3V engines. The best that I have been able to find, is that the Gen2 V8 engine in the ST is substantially the same one that is in the Mustang GT of the same year range. HP rating on the ST is 292, and on the Mustang GT it's 300. While there might be some slight differences, the MAF is the same, as for a short time I installed a C&L Performance intake system from an '08 Mustang GT onto my '08 ST and it ran great with no CEL's. With the weight of the ST and rear gearing you can always use a little more power. :grin:
I guess I give these 4.6 engines a little more support, as the power has increased since they came out in '96 I think it was. It would be great to hear if anyone has done engine mods though. An STA owner on another forum I believe took his 4.6 out, installed a 'built up 5.4" and is working out the kinks of supercharging it.
I thought I while back Bob C. had done some searching in his area for shops doing engine upgrade work. He may have some info to share from that, but I'd have to look back at those posts otherwise.