Exhaust sizing 170 1966

[Frokost]

I'm lucky enough to have inherited a 1966 half cab with a 170 that's been in my family since new, but it has a rusted out header pipe. Unfortunately the rig is not in front of me right now or I'd do some measuring and figuring on my own. Anyway, I am trying to buy a kit for the exhaust system past the manifold (and perhaps even the manifold) and looking for some advice. I see CJ Pony has a 2" kit but from what I've heard, the old system used 1 3/4" (or at least does past the muffler).

My questions/concerns are:
1. Is the old header pipe truly 1 3/4" or is it 2"? Similarly with the exhaust manifold. If it's 1 3/4", do I need an adapter for the old exhaust manifold or does it still work OK? It's kind of hard to find decent options for the 170 so I'd prefer the true (or close to it) system if possible but I'm unsure whether this 2" is alright.
2.When to replace the exhaust manifold - I didn't observe any cracks but by cylinder 6 there's a broken bolt in the exhaust manifold (held together with a vice grip of course). While I have the exhaust pulled apart, I was debating tackling this issue too but I'm curious whether I should just keep the old exhaust manifold if it looks good and just slap on a new gasket.
3. switching to headers or remaining with the old exhaust manifold - I'm leaning sticking with the old but thought I'd get thoughts here.

Hoping people can help me with these, particularly point 1. Thanks!

 

[okie4570]

Yep original 170 exhaust was 1 3/4".

 

[B RON CO]

Hi,I'm pretty sure the original exhaust manifold will bolt up to the 2" exhaust. They connect with a "donut", which is the exhaust gasket. The donut sits on the down pipe and pushes up into the manifold.
Unfortunately a broken ear on the manifold ends is way to common. I believe the problem is trying to quiet down a leak when the cause is a warped manifold. The manifold is not going to bend so overtightening breaks the ear on the head.
If you remove the old manifold you need to get it surface ground at a machine shop. My old machine shop did it on a big belt sander.
The other option is to get a new Mustang exhaust manifold with a 2" outlet.
Good luck

 

[bmbm]

My 66 has a 2" exhaust system if I remember correctly and the 2" should be better for performance from what I have heard. You can get some information on six cylinder exhaust and a source for headers on fordsix.com.
Congrats on your 66.