To answer your first question, you can always reach underneath the truck, with wireclippers, and snip the brake wire back to rear wheels to release the e-brake. Oh, just kidding.
release lever is missing? It' s not hard to fix. You (or someone who know how) can go to junkyard get replacement and install okay. Mechanic could do it easily enough. Part shouldn't cost too much., especially used.
But to release brake without lever?? All the lever does is to push or release a spring which is holding brake on. A large screwdriver might be able to do same, but get some guy who knows what he's doing.
