Great assembly Bulkheads

Ive managed to shear of a screw head in my front bulkhead.
It was the only stainless steel screw on the truck :019:
someone once said to me never, never use stainless, use hardened steel, They may rust but they don't snap. Guess I wasn't listening :032:

my idea was to enlarge the skid plate holes on the bulkheads to M4.
has anyone done this, and is there enough material on the bulkhead to take the enlargement without risk of it splitting?