I'm fixering my M715. With roof flashing and urethane caulk.
PO hacked up the firewall. A lot. It's 1/2 Jeep, 1/2 Chevy, and 1/2 Ford. And another 1/2 spiky booger welds. It leaks a lot, and I'm sick of water sloshing around in my speedo and freezing in the headlight switch.
So, I could cut 5 little plates and weld up the holes (air intake doesn't exist any more), then chase weld porosity and sheetmetal screw holes (grille is held down with a couple rubber-washer roofing screws)...or I can block off the whole thing, put the grille on top to look pretty, and forget it.
It's raining outside, and this is working great so far!