help needed with 904

Never messed with a automatic transmission before more than putting in a shift kit a long time ago I think. I have a free Craigslist 904 transmission. I have a TCI torque converter that is new in the box and been sitting in the Box for probably ten years or so but still brand new. The transmission was rebuilt like 10 years ago and barely ran for a small amount of time and reverse went out? It's whisper clean for being kicked around someone's garage for the last 10 years so that's the story. I have a mucky old 904 transmission Outback that does have a slip yoke and the dipstick and looks like some of the kickdown linkage. I have a quicksilver shifter I intend to use with it. I'm converting from my 4 Speed to an automatic.
Building a small motor for my wife to drag race the car so it will be a race application but honest very extremely strict budget this must be one of the number one considerations.
I guess my questions are where do I start by taking this apart obviously I want to put a shift kit in it or some sort and open it up and try and see if there's anything wrong with it or maybe I need to replace it soon SEALS or something because it's been sitting so long? anyways it needs to be dealt with. Thank you for any and all responses...
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