The options are endless.
Easiest and cheapest swap probably is a 2,0 Zetec ITB (preferably a ST170 basis), good for up to 200 bhp without touching the bottom end; turbocharging will get you far beyond 300 bhp when you're willing to invest some money on the bottom end.
Mostly the same work but the better engine: 2.0 Duratec HE with ITB, also about 200+ bhp with the right setup
2,3 16V might be an option (RS2000 16V based engine). Nearly nobody tried to get some power out of these engines, but I think with cams and ITBs you'd also see ~200 bhp. Plus it was longtitudinal mounted (in the last Scorpio) from factory which makes it easier to put in when buying a whole donor car.
Cosworth 24V: Over here you get these quite cheap, mostly bulletproof engines, good torque but there's mostly no tuning parts available, especially a set of sports cams would be great to have as the setup of the engine is for a comfortable cruiser mostly.
And there's many, many more options. How about an inline six M3 engine? 286-360 bhp standard.
Or maybe one of the crazy japanese engines (2JZ etc.) I don't know much about?
The choice is wild these days, but again it comes back down to goals and budget. Some swaps will be cheaper than others and easier than others.
And of course ease of finding a suitable transmission or adapter within his budget or does he want to stick with whatever trans he currently has.