Hey I’ve read on multiple posts that mopar performance and other brands of slant 6 headers except Clifford’s fit 66 and earlier a bodies. But I haven’t really heard why, I was looking to maybe buy some mopar performance 6 into 1 headers on marketplace, for my 65 valiant but wasn’t sure if I could make them fit. Is their clearance issues and is there anyone who’s modified the headers to make them fit?

They will not fit because of major interference at the steering linkage if I remember correctly. Could they be made to fit? Not without a major rework. Plus they hang pretty low below the car. Better to get a pair of Clifford shorties or Dutras.

_________________
2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

As far as I know, the only headers that fit the 66 and older "A" bodies are the clifford shorties, or the old, discontinued long tube Clifford's, or the Aussie Speed.
Then there is the differance between the 170 and 225 engines. The clifford shorties will not fit the 170 without modifications. The same mod is required with the 225 with power steering. The front collector hits the steering box. The Clifford shorties will not fit the 170 with power steering without "major" mods.
The old Clifford "long tubes" are different for the 170 and 225. Trying to put the 225 headfers on a 170 puts the tubes almost on the ground, and the 170 headers on a 225, the tubes hit chassis/steering parts. The Aussie speed headers are said to fit both the 170 and 225. I have a set of them and on the 170 they sit very low to the ground. I have not tried them on a 225, yet.

_________________
Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

That's almost 180° from reality, that said, I did do unmentionable things to a MP 6-1 to fit it in My '64 GT. I heated/beated/hammer-welded it to fit, & it's still super close to the box/coupler/pitman arm/inner tierod, ultimately I plan to yank it & cut/move the tubes now that it's the pattern itself. The 2 main issues are the engine sits ~1" further forward in relation to the frt steering/suspension, and the frame rails are almost the same tighter each side moving the steering gear that much closer.
Oh, I pulled & reinstalled that thing 12× before I had to this point.

What are you trying to build? Street car? Race car? ...

I wasn't going to admit to it but many years ago I took a set of 6 into ones and "made " them fit a 65 valiant (4 speed) They were cut, rewelded, beat ,cut again,Tubes moved & beat some more.... You get the picture. Then they hug terribly low. I eventually ended up with a set of Clifford Long tubes that fit like to were made for it. If you consider the headache factor, almost anything else you choose would be better than the 6 into 1

_________________
2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

It’s a street car mostly stock cruiser, just trying to get a better flowing exhaust and nice sound(and they look cool), figured it might be worth the trouble since the header is pretty cheap 150$. Wouldn’t be my first choice but don’t really want to drop the money for the Clifford’s. Thanks for the warnings, wanted to see if it’s been done before I get myself into this.

Thinking about it I might just increase my pipe to 2in from the manifold for now probably better just to wait for a better fitting header

Truth is if those headers are in good shape, I'd buy them and sell them for $300 or so and then put that money towards what you want to get.

_________________
2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6