Has the system already been evacuated and charged?
If not, you should most definitely replace the filter/drier.
If the lines were left open long enough to replace the compressor, it's not a big deal as long as you evacuate the system properly.
You did not indicate whether or not you are converting to r134 at this time. If you are, there are other steps that it would be good to take at this time.
There is really no need to replace the H-Block (expansion valve) unless it is leaking or you are changing to r134. Actually I changed to an r134 Hblock when changing over my 240D. The new H-Block subsequently leaked and I replaced it with a new R12 H-Block that I had on hand. I could not tell the difference in the cooling effect when changing the H-Block.
Summary; if there are no leaks and you are staying with R12 and have yet to evacuate the system, I suggest you replace the filter/drier, pump down, ensure that it will hold the vacuum for several minutes(gross leak check) then charge the system.