i use hooker competition long tubes ceramic coated (#6901) in my 67 fastback. Engine is a 331 stroker with tremec tko. The headers fit absolutely perfect. My are polyurethane motor mounts from prothane (#6-503) and they fit with the headers too.
But, cable clutch is a no go. I use a JMC hydraulic clutch setup.
FPA longtube headers (Ford Powertrain) is what I put on my 67FB with 331 stroker and magnaflow X system. The tubes are 16ga. and flange thickness is 3/8", they are extremely well built and you'll gain an extra inch or more of ground clearance as they don't hang down any lower than your frame rails. They will cost more than hookers though.
I also suggest Hooker Super Comps. You do loose about an inch of ground clearance... which for me drags on every speed bump. My car is lowered about 3 inches.
Kevin
+1 for Hooker 6901s
I don't have a T5 yet, but I know they fit from research, and I found 6901s (Hooker Comps in general) to have more consisitent quality than Hedmans I have used.
2 tips that you should know... Not so much good or bad, just things you should be informed of before deciding on a Hooker header.
1: The Supercomp headers are not so much better than regular Comps for general use when it comes to added HP or anything like that. The main, and almost only, difference between SBF Comp and Super Comp headers is weight.
The Super Comps are lighter for racing. However this makes them less desireable for street use because all of the metal is thinner. They are more delicate and prone to shorter life.
2: If you feel you must have header coating, then make an effort to buy the headers uncoated and have them drop shipped or send them to a second hand coater... Jet Hot for example.
Hooker only coats the outside of their headers, and they are notorious for poor quality coating where they do put it.
I have read many posts about the coating flaking off or headers rotting from the inside out.
Jet Hot coats every surface, in and out, of the header and is known for quality and svc.
They also carry common headers, like 6901, in stock so you can order the whole thing from them with one shipping charge. Last I checked, a Hooker 6901 from Jet Hot, coated, cost slightly less than 6901s coated from Hooker.
That said, I am a member of the "coating is snake oil club"...
Dave