Which 5 speed do I get?

I like the modern tremec and I also like the Passon if it ever gets released. Ive been reading up and the TKO-600 now comes as a direct bolt in for my 1973 Duster for 3700 shipped to my door.(no cutting of the tunnel is key) Before I drop a ton of cash on this thing i want feedback from you guys. Positive or negative I dont care, I need to make the right decision. Thanks in advance