Ok, it's probably going to depend on how you decide to pop off the stack. Given "N1 N2 o" in RPN where N1 and N2 are the numbers and o the operation, the LTR should be "N1 o N2".
Yes, '/' would need to be 4. And yes, the second one poses the problem if there's no indication of order being important on an operation ("a op b" not being equal to "b op a"). Chipmunk's got part of the problem with associtivity in his 171 char solution, but I might need to restate the problem to handle this concept; at the time, I was only aiming for a general solution assuming that order didn't matter.