Just do what the PO did with my K code back in the late 60's and early 70's. You still have full exhaust but when it's track time you just unbolt the plate and you have dumps

 

thats pretty messy looking....

 

She is.

Currently under full restoration though.

 

A little off topic but somewhat relavent. A turbo unit quiets down exhaust so, you do not need to run muffler in locals where exhaust emissions are not monitered. (The turbo is not on a mustang but 7.3 diesel, and has 3 bends from turbo to dump. which is in front of rear wheels. Turbo and 3" pipe were self installed.
Check your state and county requirements.
Tom

 

I didn't know they was illegal, I had my h-pipe hooked up with some flows clamped on them. Loud as hell.My 67 ford truck has a 352 FE, and has turn downs before the axle..... louder then hell.....