Here's what I recommend from our product line for your TH350 build:
~ Part number HP3288, premium master overhaul kit, includes: seal kit, gasket kit, sealing ring kit, (10) red forward/direct frictions, (9) forward/direct steels, (5) red low/reverse frictions, (5) low/reverse steels, (3) red intermediate frictions, (3) intermediate steels, Kevlar intermediate band, filter, adjustable vacuum modulator, thrust washer kit, bushing kit, governor screens.
~ Part number HP3279, direct drum with 36-element intermediate sprag and heat treated custom races.
~ Part number 44815, low/reverse roller clutch
~ Part number HP3255, steel case positioner assembly, helps prevent premature failure of low/reverse roller clutch
~ Part number HP3215, transbrake valve body kit, reverse shift pattern (P-R-N-1-2-3)
Combined with proper attention to detail and proper build procedures, these parts will help your TH350 easily withstand 650 flywheel horsepower. If you want some additional safety margin and room to grow into, then our HP3214 billet input shaft w/custom forward drum assembly is a good option. You don't have to have this item for 650 HP, but if you're thinking you may increase power in the future then the billet shaft will get you additional durability well into the 800+ HP range.
We also offer an NHRA-approved locking dipstick and filler tube under part number HP3235. Our deep cast aluminum pan is also a popular option available under part number HP3280.
If you want to avoid a transbrake and stick with a full manual valve body then we offer part number HP3210, which features a forward shift pattern, and part number HP3210R, which features a reverse shift pattern.
I can PM prices to you if you need any of these items quoted. Thanks!