K-H brake swap done, but doesnt stop!

Agreed, the fluid volume should be adequate for the early a disc brakes. However, if the rear brakes aren't locking up on gravel while standing on it, I would take a second look at the proportioning valve and rear brake adjustment, etc. Definitely check the caliper pistons, I sometimes drive a Tacoma on occasion with the infamous four piston calipers. When those things get stuck, stopping a sled is easier...