Since you are in the process of redesigning this you may want to take a few things into consideration.
If this 3 phase 4 wire delta system only uses a two winding(open delta) transformer bank to derive the system there may be limited capacity from the source. It depends what it was initially designed to serve. You could have a situation where there was limited three phase loads and a lot of 120/240 single phase load and the A-C windings are a larger unit then the high leg winding.
There are other cases when a full delta transformer is used where there maybe is a lot of three phase load and having that extra 240 over 208 volts has advantages. I mostly find this desirable where there is a lot of motor load and limited 120/240 single phase load.
You also run into situations where the facility is remotely located and POCO doesn't have all three primary phases in the area - they can still derive a three phase system where needed with an open delta transformer bank.
If you are doing a major renovation, and is more desirable to have a 208/120 wye system, maybe see what it will take for the POCO to supply it - may be worth it in the end. Existing gear and conductors should work with either system. You will need to adjust any existing motor overloads/ confirm that any existing 240 volt loads are still usable @ 208 volts but most will be fine. Something easy to forget- HVAC systems may have control transformer that needs taps changed from 240 to 208 supply.
. On a 3phase 4 wire 240/120 delta, your "neutral" conductor is in fact between A & C phase and will be 120v between those phases. It is also your grounded conductor and there would be 208v between B and "grounded conductor".( if it is a 240/120v 4 wire delta.)
