On a 66 Mustang were thinking of adding gt40p heads to a 331 with a cable clutch t5. Has anyone had success not burning up cables with long tube headers that fit gt40p's?

 

Good luck finding long tube headers that fit consistantly. The only companies I know of that make headers specifically for GT40P's are Doug Thorley and FPA, both of which are very, very expensive (but very nice). I really don't recommend P heads.