67 Barracuda project... narrowing 8 3/4 rearend

Yeah, I was taught to have the center of the pumpkin offset. The U-Joint works best when it has a little bit of angle. This is counter intuitive to what you would normally think.

Are you tied to the QA1 Rear End? For the money, I would invest in the RMS Street Lynx. Either of these kits will require the spring perches to be in the same place as the factory rear end.

Paul Horton Welder Series is a Canadian company that makes all the brackets you would need to install the 4 Link yourself.

Last, I would recommend the Ford 9in because of all the aftermarket support. It seems like you are ready to spend some money on this project and you are not trying to keep it original. I think 650 hp is the limit of the 8-3/4", and might be into Dana 60 territory.