Originally posted by Alan
Now the questions:
1. The 99-up Cobra IRS bolts up to the factory supension locations. I know this is an entirely different rear suspension setup than the stock 4-link. If I were to eventually compete on a national level where people actually care about what you have done to the car...will this still be legal in SM?
2. I heard tubular k-members (regardless of whether or not they retained stock suspension geometry) were not allowed in SM. However I have yet to read this in any rule book. True or false?
3. If I have to use the stock k-member, what about tubular a-arms? Are bolt-in braces that strengthen the stock k-member allowed? Do I have unlimited choice of bushing materials?
4. The interior: do I have to retain any of the factory interior? I plan on just keeping the dash and headliner...door panels will be replaced with aluminum sheet and everything else will be sold.
Thats about it. Everything else is pretty clear. However I do find having to retain a metal trunk lid is strange. Finding a rust free perfect condition trunk lid without holes for luggage rack or spoiler can be almost as costly as purchasing a fiberglass unit. Just find this a relatively odd rule. 
First thing to note... if don't see the rule you want in SM, then you have to go back to SP... if you don't see it there, then you go back to stock. Every class is subject to the rules of the classes before it, with the allowed modifications that the particular class allows.
1) Suspension is OPEN as long as it bolts to the factory locations....ie, the oem IRS is legal.
2) True, k-members are not allowed
3) A-arms are open, bushing material is also, IIRC
4) Interior must remain stock except for the seats, steering wheel, shifter. The backseat may be removed... you cannot have AL panels for doors. All saftey equipment must stay there also, IIRC. Cages that conform to the SCCA requirements are also allowed.
Some of the rules may seem strange when you think about the car you're preparing...in your case, a Mustang. However, you must understand that the rules are written as to cover ALL cars, and not to make specific rules for each car, which would be a logistical nightmare. Things like the K member rule suck for Mustang owners, but to write a rule which allows the k members that are available to Mustang owners would be impossible to write so that most other cars couldn't basically tube frame the front of their cars, which would be a huge advantage, and is a mod that you can do once you reach Prepared.