I was looking at your build and noticed the curved bars you used. I did the same on mine... what a pain those were! I also considered a spool for the rear end. I was told by many on this board, as well as most I talked to outside it, and the consensus was to run an open diff. The main reasoning given was that open is far more controllable at high speed with a loss of traction. Personally my logic told me a spool would be more stable but after thinking about it I was sold on an open diff. I have yet to run, so for me the jury is still out, and Im sure there will be may opinions on both sides.
I am also running rear drums only. I am sure they will not stop the car on there own, but thats what the chute is for right, heh.
By the way, I love the build. It looks great, I can wait to see it all come together.