I emailed Kelly over the weekend and here is what he had to say. (perhaps evident just from the pics to many but not me.)
I have never seen the brass frames in person but it was my understanging
from reading several build threads that you had to cut and glue on allexpensive in the raw material form so I choose aluminum.
Frames are $78 plus $6.50 each. He is more active on the yahoo P:48 forum. (I hope he doesn't mind me divulging this info but it seems like this would only help!)