I just posted this as a reply to another similar post, but I wanted to share this as much as possible to make it easier to find. Before buying these headers, I tried to find forum posts of other people installing them on older trucks but couldn't find any. So I'm sharing this again here in hopes that it'll help someone else out if they're looking into it.
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I recently decided to bite the bullet and buy a set for my 97 even though they aren't listed as fitting. They do in fact fit. I was worried that maybe they wouldn't fit since the chassis on a 98 is a lot different than a 97 or older truck, but there's still plenty of clearance with these on. There's plenty of clearance around the steering shaft, which is what I was most worried about. Unfortunately, I can't say if the y pipe on my truck would've bolted up because the bolts were seized in the manifold so I cut it to get it all out.
Before buying these I did a bit of research. If you look up stock replacement exhaust manifolds, Dorman has the same part numbers for a 97 and 98 3.0 ranger. But, on the driver's side manifold, they have the two different EGR connections (the 97 and 98 use different EGR fittings on the manifold, so Dorman just makes one that works for both applications). This leads me to believe that my stock y pipe would've bolted up, since the stock manifolds are interchangeable between the two years (other than EGR).
However, I also tried cross referencing an older Ranger, a 94 3.0 to see if those manifolds were still the same part numbers just for kicks. Those did not match part numbers, and they did look a little different. So, there's definitely a possibility in some older trucks that a custom y pipe will need to be made, along with the EGR tube (if you're keeping EGR). But, neither of those are a big deal.
The only clearance issue I ran into was that the throttle cable ended up being very close to the header, so I ziptied it out of the way. And on the passenger side I zip tied some of the vacuum lines a bit further away from the header too. Those are the only things I had to change for these to go on my truck. I can't guarantee that they'll fit in all older trucks, but I hope this helps.
Here they are in my truck, and I also added a picture of the EGR tube I modified to work.