Delica Canada | Mitsubishi Van Club

I have a 1995 L300 4x4, its a 5 speed manual with a 4D56T in it. The engine is starting to get old and will need to get pulled out at some point (i think the piston rings are worn because it likes to smoke a lot, especially when starting). I was wondering if it was worth it to put the original (rebuilt) engine in it or if there was a betetr replacement option? Power isnt that important, the stock amount is enough, i just want better fuel efficiency.

Thanks