Thanks for the input, everyone. You all confirmed what I was already thinking--an engine swap probably isn't worth it.
A diesel engine would be cool, as would a manual transmission (I think I'd do an NV3500 or NV4500 instead of the T56, though). However, I'd only consider doing those if I had to replace the engine or transmission anyway, which I'm hoping won't be anytime soon (as the car only has 83,000 miles on it right now).
And yes, I fully intend to do some aero mods and some engine/trans tuning as well, and I already have a gauge installed. In fact, I had one soldered in before I even changed the fluids or filters.
We've averaged mid 60's MPG with our Metro for several years now. If we can get half of that out of this wagon, I'll be quite happy.
