A/C: reciever-dryer question

[dw1]

I see 911-579-939-03 & 911-579-139-03 listed interchangeably on several parts web sites (including Pelican), but the PET indicates the "-939-" is the correct one for my '87 3.2.

• What is the difference (if there is one) between the "-139-" and the "-939-" as both appears to have o-ring fittings and not the old flare fittings?
  
  
• Also, is one of these better than the other for a system that has been converted from R12 to R134a?

Thanks in advance.