Nial the crankcases of the 917 were cast in either magnesium or "elektron" which is an aluminium/magnesium alloy, so pretty exotic.
I have seen people trying to sell 917 brake calipers at amazing prices, but not sure if its just for the historic value or materials.
As for LBCs, rear bumpers for TR4s are available, but 3 times the price of fronts, for some reason.
Simon.