Forgot to mention a couple things.
Most rvmb are set around 125 psi line pressure. Most transbrakes are set 170-200. My transbrake is from tranzact as well.
My motor should make similar power to yours and Joe told me that the 904 needs at least 170 psi line pressure to live at that power level. You can buy the higher line pressure spring from A&A trans.
Also you need 5 clutch front drum if you don't already have it.
Also while this is controversial, some cars have no sprague trouble.
I have talked to some other racers who after a stroker motor build claim they cannot keep one in the trans afterwards.
There is a relatively new 30 element sprague available for the 904 that can handle much more torque. It is a caged dogbone design.
You might need that too.