I think it'd take a bit more then 6 grand to get a crate motor and actually get it to work. The cheapest crate motor (from Summit Racing) is $3500 from Ford (a 345 HP 302), but you still need to convert it to EFI, a V8 computer and wiring, cooling system, either a new V8 tranny or a conversion bellhousing (I don't think the stock ST tranny bolts up to the 302, although I might be wrong...think I am actually), move the firewall, engine mounts, and other stuff.
Could you fit a V8 in for under 6 grand? Yes, you can, but you'd have to get a used engine, rebuild it, and do just about all the work yourself or have a good buddy who would do it for cheap or free. Emissions, inspections, laws and regulations, and computers can make it difficult to really do some stuff these days.
You know, about those STS and other rear mounted turbos, I'm not convinced they are all that good, and certainly not better then a traditional engine compartment mounted turbo. For small turbos, it may not be so bad, as the piping is small; but step up to medium and large sized turbos (or two) and a rear mount just doesn't make sense. Maybe thats my flawed thinking in this issue, I want a big turbo with a big FMIC matched to a 6-speed. There isn't alot of room underneath most cars and trucks to mount larger pipes. On the ST for instance, you can't run true dual exhaust because of the lack of room, so where would a second pipe for the turbo outlet go? About the only other aftermarket tuner that comes to mind that hasn't used engine local turbos is Lingenfelter, with their twin-turbo Vette.
I call the ST the wrong vehicle for that much power because the platform never really was meant to see that much power, and it can be dangerous. I don't think I'd want that much power in a truck as high as the ST, or with its outdated suspension system. That's just me.
