I am interested to find out what you end up with. I'm currently putting a 2006 5.7L Hemi in a '73. I have the 8HP70 transmission. I'm using the Holley motor mounts, trans mount and ceramic coated cast manifolds (from Holley) and the Holley aluminum cast pan. I'm also using a Steer & Gear refurbished factory power steering gear box, factory K-frame and Torsion bar setup. The difference being i've got the longer R/T pitman arm and then a longer idler arm out of I think a B Body. My first trial fit, the exhaust manifold hit the steering box pretty significantly. note in the attached photo near the drivers side shock tower.
At the time I ordered the parts, Holley had a Blackheart Header that they listed, but have since withdrawn any mention of it on their website. The header is no longer listed as a Hemi Swap option, nor is the cast exhaust manifold for this combination. I am not even sure the Borgeson unit will clear, but am going to try fitting it up again. This was the first test install, so I expected interferences to show themselves. The AC compressor also hits the K-frame. I've modified the K-Frame to remove interference and hope to get it trial fitted again.
As for headers, TTI had a lot of "conditions" listed for their headers to work. Unfortunately as soon as I added the longer fast ratio R/T pitman arm, that eliminated that option. I know that doesn't answer your direct question, but hope it helps with your decision process.
