I would venture to guess that you'd have to fabricate a pedal setup, since AFAIK there was never a 126 sold in the U.S. with a manual tranmission (there's a couple Euro 126's with manuals, but they're extremely rare). I don't know on the 116's, though.

Beyond that and the shifter linkage, the biggest issue might be figuring out where to put the clutch master cylinder...

That's all that readily comes to mind; sounds like you have the engine/tranny side planned out.

Good luck!