When buying built, see sticky above and find out how much of it has been done. The general consensus seems to be Alto reds for clutches and band, non Kolene steels. If you are directing a build or DIY, see minimum for a low 12 second tranny below. Brands for valve parts, I haven't a clue.
The Alto band is wider than stock, so it makes sense to upgrade the servo piston to get a similar or greater clamping force per unit area.
As you probably know, these are touchy beasts. If a person is bucks up, it would be logical to buy one from an expert.
I'm a newbie; anyone with better or more complete info, please jump in.