904 manual valve body

The bolt in sprags aren't any stronger than the unit in the vehicle, they are just easier to change. Not worth the effort if yours isn't messed up.

Next I'm going to tackle the low/reverse band apply question. I don't run one in my car. If you load the driveline (powerbrake) before you launch everything is already "set" there's no need for any additional holding power. The problem comes if you have a driveline failure while under power in first gear. This is the only time the sprag is holding the drum. If it happens you need to remove the trans and inspect the over running clutch (sprag) before you put the car back on the track. While O/R clutch failure isn't common, and unless you are using a trans brake I wouldn't fret over it, it does happen and for that reason I recommend an SFI trans shield. The aluminum kind, not the carbon fiber type, or a ballistic blanket will do also.