Torqueflite 904 450HP please help me !!

I'd make sure and use steel planetary gearsets if your using nitrous cause I doubt aluminum ones would last. If it were me I'd check www.bulkpart.com for the rebuild kit. Neither of those kits say they have bushings and a rear sprague roller kit. That's a must have when building a trans IMO. If I remember right Bulkpart has a complete kit that includes all the small parts that aren't included in the kits from summit and the price is around $250

As for the converter. I've had good luck with Hughes converters but they don't usually stall as high as their rated. You can get a custom built for your car torque converter from PTC for the same price as the Hughes.