Quality triptychs like this are hard to do. I know Joanne Callis did some good work in that realm years ago.
Probably your BEST bet would be some kind of registration process and a VERY good 4 blade. The masking is the easy part really. It is getting every frame to line up that is hard.
I have heard of people using large 4 blades and 3 different enlargers. You set each easel for one image and use a registration system to move it along. You need BIG 4 blades though.