A500/42rh

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You may want to do a search and read a couple of old threads about the mods needed to do this swap before jumping into that pool. Picking a tranny is the least of your problems...
 
Pre-1994. That is, you want a full hydraulic valve body. Beyond that, cores are pretty similar. The basic transmission is a 904, so all the typical 904 performance mods apply. Also, because these transmissions generally came behind a 3.9 V6 all the typical 904 performance mods are REQUIRED. Not shocking news. I wouldn't bolt a 120K mile transmission behind a stout 360 and expect it to put up with a lot of abuse (although you might be surprised).

A high stall, heavy duty 904 lockup converter will also cost some $$$ as it will be a custom item. Good convertors cost no matter which transmission you chose, but it will be a requirement here. Not a lot of cheap "so-so" converters unlike a 727.

The overdrive makes the tail shaft section of the transmission considerably bulkier, and it will not fit into an A-body rear cross member. Therefore some modification and fabrication will be required for a quality swap. Again, nothing cosmic, but expect to spend a few hundred bucks if you farm it out.

I plan the same swap and have a core waiting to be rebuilt. I contacted SMR for their recommendations based on my intended package (moderate 318, 3200# car, 4.10 gears) with some room to grow (or a +150 nitrous shot). They recommended their 10 3/4" 3000 RPM flash stall, lockup Pro Sportsman converter http://smrtrans.tripod.com/smrtransmissionsintro/id37.html About $600. For the transmission, they recommended their Pro Sportsman rebuild kit $540 http://smrtrans.tripod.com/smrtransmissionsintro/id10.html and Valve Body Upgrade Kit $200 http://smrtrans.tripod.com/smrtransmissionsintro/id14.html

So, you can get $2000 tied up in this swap without trying too hard. Perhaps not out of line IF you are planning to rebuild a 904 with a custom converter anyhow, but something to consider if you'd be pulling an otherwise healthy transmission in search of a couple MPG. Sure, it can probably be done cheaper, but you'll have to determine what is an acceptable compromise.
 
Herc chief, as long as you're here and in the mood to answer questions (thanks for that) I'm gonna hijack and ask one of my own. Do you see any reason why the A500 guts and tailshaft/housing won't swap into a 904 case? Just curious...
 
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