Auto Transmission options

[sdntive]

I have a 73 Challenger with a 318 mated to a 904. Im going to get the engine built up by IMMengines which should make around 600hp and 550ftlbs of torque. Im looking into what would be the best 4 speed auto to mate with this built engine. an an a500 be built to hold the power and from which company or do I need to upgrade to a a518? I really dont want to cut up the floor to fit the transmission and this is mainly for street use with very little drag racing.

[brads70]

First off , welcome to the forum!
So.... let me get this straight? Your getting a 318 built up to 600hp and 550lbs ?  hand-grenade?
The strongest factory auto is a 727 , they were available for both bolt patterns , SB and BB. if you want overdrive with those look into a gear vendors OD kit.
If your wanting a 518 look here....
http://www.cuda-challenger.com/cc/index.php?topic=84774.0

[sdntive]

Yes I know that I would be pushing a lot out of the little 318 especially since it is a 40yr old block. Ive been snooping around here for a while reading about the a518 swap Im looking to for companies like PATC or SMR, Ive read the bad post about Keisler and I would like to keep this mostly Mopar. So mainly Im looking for options for companies who built transmissions to hold this much power for street use