Any off the shelf header on an early A body (63-66) is going to be tough. Basically you have to understand your framerails are 2" closer together than later A bodies. I have never looked at a set of TTI headers on one of these but can only imagine how tight the fit will have to be.

I would recommend running a BOBSPROFAB tubular front k-member with rack and pinion and coilover shocks. This will move all the problems out of the way. Then you have a lot more room. But, the best headers are going to be a custom built header. This is not inexpensive and I don't want to BS you in to believing it is. But, after you do this you would really have a nice front end and headers that would truely turn your somewhat basketcase Barracuda into a really nice user freindly car. I feel I can say this because I know these cars well. My car was a total headache to work on until I made these upgrades up front. Now I would not trade it for any other A-body.

PM me if you have any detailed questions

Leon