I have a very old Sabco Brew Magic on which I recently upgraded the burners.
It runs the propane through the frame and has 1/4 turn ball valves (I think they're ball valves) on 3/8 inch black pipe to each burner, just like you mentioned. Works very well.
The most difficult thing to find was the combination of fittings to go from the orifice tube on the burners (3/8 flare or something very similar) to the black pipe (3/8 pipe thread).