Do you have the rulebook for the race series you want to participate in? Would be an interesting read. I wonder if since it's a Ford part that came in OEM vehicles if there's a loophole on what 'stock' is
Yep, that's the issue. The rules say we can use the diff if it was available for the year/make/model or generation of the car, but it excludes the Boss/GT500/etc since it's a specialty/high-performance model.
The gear rules are a similar story. We can use any factory-offered ratio for our year/make/model or generation, excluding specialty models like Boss 302. We had an idea last night that would possibly allow us to use 3.73s...we think those were offered in the 05-09 Mustang GT, which would make them allowed for our car (same generation). But we think they're too low for the job anyway.