for BX1880 I sw this on parts... K277143174 as the brake pedel assy... $80 CDN. Don't know what the Messicks part is....
Before you have someone 'cut and weld', make a 'model' out of wood. Take some measurements, cut plywood to look like the 'profile/side view' of the arm.drill.hole where it pivots,screw into workbench and mark floorboard on bench. move arm like you're applying brakes. Might take a couple of tries to get it accurate. When you do, make a 2nd one, cut THAT one and see what happens.
My gut says when you cut and lower, you'll need to tilt the short 'pedal; piece toward the back a lot.
A neighbour did this for his tractor's clutch pedal as he wasn't as tall as us normal guys.....
at least wood is cheap, you can make lots of free tries BEFORE welder guy modifies the $80 part.