Either should work fine and work the same. The left side is the only significant difference. Both share all the same mountings, less skid plate. The left side may bear upon exhaust installation. The single humps were used primarily for catalytic converter clearance on TBI trucks. Even tbe single hump crossmember will accomodate some factory duals. I notice on my 85 K30, factory double hump and stainless steels duals (OEM and still original from 1985), that the single hump would clear the LH exhaust pipe as it is tucked in rather close in the frame rail "C" section.
I have both crossmembers availble. Let me know if you need still.