TH400 Rebuild Advice

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Hi all,

I need to rebuild my Turbo 400 to handle up to 600HP to suit a new motor

The trans seems stock. I have upgraded the torque converter only at this stage.

Before I approach some trans rebuilders I want to get an idea of the parts upgrades I need to strengthen it so I can get value for money.

I want to keep it manual/automatic setup. I plan to remove the trans myself and take to the shop.

Im just a bit confused with the terminology... corvette servos, direct drums, 34 element sprags, shift kits etc

Thanks for any advice