Longtubes are non-existant if you want an "off-the-shelf" header. Well, I shouldn't say that because I believe Hooker makes a longtube with 1-1/2" primaries (yuck) for '80-'95 F150s that fit, but I am personally leery of their quality. It's a "cheap" header if you know what I mean, and a bit undersized IMHO. Your only real option for a longtube is to have something built, which is gonna cost some bucks. I have a set that was custom built for my truck, but I've not yet installed them. Should have 'em on within the next two months or so, and I'll post the results...
Moral: if you want an easy bolt-on, many of the shorties out there are just fine. But if you absolutely have to have a longtube, then you'll probably need to go with a custom header.
Hope that helps.
- Kevin