Fox body Mustangs are not money pits if you're looking for power. Like LS-powered cars, these are the absolute cheapest & reliable engines to make significant power from.
The problem here is that your friend bought a POS. There is zero reason to spend $10,000 on the 4.2 or 5.0 V8s just to make the motor ready for boost. You could dump $10,000 on a completed Fox-body now & find one that's running on a small, boosted setup.
$10,000 dumped into a Fox body is enough to make a large amount of power, not 450whp. The key is starting with a decently maintained V8-model.
I don't have to own one to know they're dependable, esp. for power. I've seen & talked to enough 4.2/5.0 owners to know they're solid platforms b/c the majority of these guys are all after big power. A rather good portion of these guys are turbocharged as well.
I haven't because this city is full of horsepower junkies, & a lot of those guys work with Fox bodys. Granted I haven't seen any new ones, but I haven't seen any less, either.