sure your engine's dying?
2 identical engines in fwd and rwd cars will feel quite different... rwd you'll get much more drivetrain losses, and a sloppy worn out clutch will only enhance that feeling of wussiness.
i've done an a/b test of a 4ac sprinter and a 4ac ae82 'rolla and the 'rolla definitely felt much more perky... but both were in top notch condition.
if i were you i'd think about just replacing your clutch, you'd be surprised how much difference it makes (even a rwd 4ac can chirp tyres into 3rd with a brand new clutch) or if you really want more power, i'd look into a 4age or similar. i'm sure it's the response you'l heard from everyone, but that doesn't make it wrong...
i'd say you really don't want to go to all the effort of putting a new engine in unless you're going to put something quality in there...