I went with the tape as I didn't want to drill the roof and the 3M tape will hold everything in place with no problem. The lower pin hold downs are mounted with the tape on the rear window no matter which way you choose to mount the hinges. The reason is that unlike the 70 Challenger, we have no panel between the rear window and trunk (it's all deck lid to the bottom of the rear window).

(I have included a picture of the louvers just sitting on my Challenger before I started to mount them. I will post "outside" pictures of better quaility later....)