I'm putting a 351 windsor in my 66 fastback. What headers will work with no clearance issues? It will have power steering and I'm not sure about the transmission yet.
Call Hooker (or whoever owns them these days) - They have made in the past a special order super Comp. long tube for your application. I talked to a guy at the track who had a stroked 351 in a 65-66 fastback and that is where he got his. Some of the primaries actually turn up instead of down, it looks wicked bad a$$..........
Headman makes shorty and longtube headers for this application. Long tubes won't work if you have a manual transmission. I think you have clearance issues with the clutch linkage. They may work if you went to a clutch cable.
Also, with longtubes you will have to get the bracket to lower your power steering cylinder.
I went with the shorty headers because I'm running a toploader with the original-style clutch linkage. Although it is tight, I didn't have any clearance issues. I was even able to drop the engine in with the driver side header installed. Once the engine was in, the passenger side header slipped right into place. I was able to adjust my motor mounts a little hear and there to fix any clearance issues.
By the way, JBA also makes headers for this swap but you would need a second mortgage on your house to afford them.