I ended up writing a dll to wrap the latest Steam SDK and linking with a DllBind (with the help of a knowledgeable modder), as the one included in UDK is old and doesn’t include many of the current features. This has allowed me to use the Steam Inventory Service and implement a system for weapon/clothing/item skins from the Steam store. Using DllBinds with the 64 bit executable is a bit tricky though, as you need to wrap the payload sent from US to the DLL to mimic that of the 64 bit structure.