I did have to hammer and flatten the pinch weld from the floor pan to the fire wall to get some clearance. The other thing to order from brewers is the clutch fork for that application. I'm running TTI headers and it's tight but doable.
I didn’t need a different fork but in the conversion kit was a clutch fork pivot bracket that changed the angle a bit and it works fine. I didn’t need to hammer the pinch weld in my 66, maybe that depends on which motor mounts you use? It’s possibly the OP might have to hammer his? I’m running Hooker super comp 63-66 headers on mine, some areas it’s tight too but no issues even after 14 years of use.
