833 OD behind a 340?

Can't say for sure. There's people who say it won't hold up. Then there was a guy in one of the Mopar magazines who had an OD trans behind a big block in a Superbird. Racers Have used aluminum cases behind high power motors for a long time. I think the major concern with the OD trans is the face that the power goes through the cluster gear & then back to the main shaft when the car is in high gear where normally the input & output shafts are locked together. I've read this tends to wear the input bearing faster because most cars spend a lot of time in high gear. This is why the size of the front bearing is larger in the OD trans.

I'm planning to run an aluminum OD trans in my car behind either a 360 or a 408 (haven't decided which one yet), but I have a close ratio aluminum case trans that I can swap in if the OD trans fails.