That is one of our
realllly old boxes. Probably
at least 25 years old.
1) That GS31 display mounted above it is obsolete and there is no direct replacement.
2) If you do add
credit card you'll want to go to a Dixmor timer so that you can do count up. If you are not doing count up with credit cards you are leaving a lot of $$$$$ on the table.
3) There isn't the room on that
door to properly add
credit card and a Dixmor timer. You will either need to add an add-on box or put in a larger box. In your case I would recommend a larger box because the one in the picture is beat to hell from people breaking into the
coin drawer. That box appears to be surface mounted so changing it wouldn't necessarily require cutting the block, although with the age of that unit I would
strongly recommend pulling new control wire when changing the box.
4) A 600gpd RO(1 2.5" membrane)with a 150-200 gallon storage tank is plenty for a 4 bay unless you plan on adding an auto at a later date.
5) I would be curious to see pictures of the equipment because I strongly suspect the place hasn't been updated a lick in decades.