easiest swap is defo a zetec, but how much power is completely down to your budget
they can do crazy numbers that are matching yb's these days, but you'll need very deep pocketc
if its just for a xr2 then on a cheap budget go 2 litre zetec with bike carbs and cams for a cheap screamer
or do a budget zetec turbo built, in something light like a xr2 either of these will be great fun