Terribly hard is a bit of an exaggeration, but I'm not exaggerating when I say the rendering section would need to be rewritten. The 2 tilesets have 128 spaces apiece making 256 tiles total, including the two null tiles. Each layer has 255 locations. The objects require 2 characters, 256 banks with 255 possible objects in each. Nifflas designed his map files to make use of every single bit. Changing the screen size means rewriting the algorithms. I guess the hardest part of that would be bringing oneself to ruin the original work, it's like programing poetry. Maybe it's just me. :)
If I still had MMF2 I'd find you the algorithms, but I only had the demo.