A T-400 is suppose to be a strong transmission, so wouldn't a $120 rebuild kit from Kragen be fine behind a 500 horse BBC?:confused:

Does a person really need to buy the $240 TCI super pro kit when a stock T-400 is already a capable trans?:confused:

I would assume there are not that many transmission parts manufacturers and that most companies buy from the same place, the consumer is really only paying for packaging.

Somewhat,
A TH400 doesn't need any fancy clutches for 500 HP. Stock frictions, stock steels, stock count works fine at that level.
So for the basic rebuild kit, yes the low cost kits are fine. Be sure they are Borg Warner brand frictions (OEM).

However,
Then you need to make some valve body mods for more clamping capacity, firmer shifts, etc.

You also need a set of bushings, a set of thrust washers, a filter, a modulator, both the bands, etc.

Most generic kits don't contain all the bushings if any at all.

I sell a kit that includes all the above, plus valve body mods and tech tips, as well as some additional heavy duty parts for about the price of the TCI kit. I also send out better direct frictions with my kit.

At 500 HP you would also want to look at a 34 element sprag and depending on your core the corresponding drum that goes with it.
The sprags are $50 each. Drums are $100.

So you easily get into a $400 worth of parts to build a reliable 500+ HP/TQ capable TH400.