Kicking around ideas for another project and was wondering whats the most cost effective OD automatic OD system I can put in a mid 50's mopar with 426 hemi around 500 hp/tq. Don't really care if its an actual mopar transmission. Just looking for readily available and least amount of modifications as possible. Opinions?

The Keisler 4 speed OD would fit the bill. Also a 727 + gear vendors OD if wheel base is long enough to keep driveshaft angle reasonable.

I'm curious... what's it going in?

A518 with the adapter Cheapest way to go & probably the easiest

I've run into a few 55 56 coronet, new yorkers etc and wanted to do something a little different. Was thinking of putting in my injected 426 with od into one. Some locals were trying to convince me into a chevy trany with adapter,insisting there will be no trany hump mods, and that the 700re (I think) can be picked up under $800 and can withstand 500 hp/tq.

700R4 is a good one to use too They don't take that much room either I've used them quite a bit in Street Rods of every type using a GM powerplant for almost 30 years now. 87 & up are the ones & the 86 Corvette case with 87up pump & seal retainer That combo with other goodies makes for a really tough trans
I did this setup behind a 500 horse 468 with a 175 shot It held up well in a 3500# pickup

I've used the various adapters over the years to put a PG behind a Chrysler engine in a race/Street car I've never had a problem with one you just have to make sure the converter is in far enough