A few months ago, I finished up my rear discs using all Toyota parts. I used solid axle rotors and calipers and some brackets I made myself. If I were starting this again, I wouldnt use toy parts. I would use the GM stuff instead. Here is why:

The main benefits to a rear disc conversion are:
1) Better stopping power
2) Easier to change a rear axle shaft.

In order to get number 2 you cannot put your rotor behind the axle flange. (The BigRocksOffRoad kit had it like this) If you have to remove the bearing to get the rotor off, you no longer have a quick axle change. Therefore, the rotor must be on the outside of the axle flange, sandwiched between the axle and the wheel. The stock toy axle must be turned down on a lathe in order to fit inside the "hat" of the rotor:

In the above photo, you can see my spare rear shaft and how it is turned to fit inside the rotor.The center hole of the rotor needs to be opened up slightly as well to fit over the centering ring on the axle flange.

Another issue is YOU HAVE TO RUN A WHEEL SPACER!

In the above pic you can see how far past the "hat" of the rotor the caliper sticks. Unless you have a funky wheel that will clear the caliper sticking that far out, you will have to run a wheel spacer.

Having done all this, was it worth it? No. As I stated earlier, the GM small calipers are a better route.