Sorry, but I think you're shootin so far in the dark I think your blind. Not trying to be mean but other then the cost of an adaptor (which if you think about it seriously for a moment) the amount of work needed, time materials skill (getting a shop to do it if you don't have the skill $$$$) that adaptor works out to be about the same cost of that labor. Now you can put a used tranny in a car but I'm not it gets rebuilt before it goes in my car (oh and it's cheaper to rebuild a 200r4 then the 42rh the whole GM over Mopar) Now you can buy a one from a performance shop or a trusted local or yourself save a little bit that way. that said youll put more power to the ground with the 200R4 and these things can be built to withstand more power then a 42rh, just pointing that out. Sorry man but GM beats Mopar in small overdrive tranny. Also if you'll willing to do that much cut and redo the tunnel, why limit yourself to a 4 speed auto when a little more you can get a 6 speed auto? It just doesn't make any sense to get less when you can get a double overdrive and better rear gears. Just Something to think about.