2 types of Doug headers for early 64 to 66 Valiants ??

When I did mine I had fitment problem as the car had to thick of motor mounts. The previous owner had installed the wrong motor mounts when he swapped the 340 in the car. He ended up putting the old 273 exhaust manifolds back on. Once I had purchased the car I tried to put the Doug's in (D450) and no way could they be bolted up. I ended up ordering Schmuker engine mounts and it was 90% better but still had a lot of work to get the linkage in with the brewers parts. Just re-centering the engine and resetting the angle of the 90 oil filter adapter was the next problem to get it to work. This car also had the 10.5 bell and mini starter.

Not sure if this is your problem but it might be something to look at and my now 65 Barracuda is running TTI's with the same 10.5 bell and it was the same amount of work to get it all to work.