Since you can't, generally, concatenate two FB of different LRECL, I think you have three approaches.
Firstly, is the two-step that you have. Cut the File 1 down to 80, then concatenate and SORT in the second step.
Secondly, there is ICETOOL, which can give you one step, but you will still have two passes of File 1 (which is what you want to avoid).
The JOINKEYS would be straightforward if you have no duplicate keys.
So, the next question is whether you have duplicate keys. Internally on File 1? Internally on File 2? Between File 1 and File 2? Some combination of these.