Thanks everyone for the replies.
My goal is to serve some 3 phase and limited single phase loads where there are only 2 3∅ 12.5kv primaries and no primary neutral. The three phase load is the largest load at about 10HP.
You would have open delta/Open delta. Open wye/open delta is more common.
Are you saying the 2 3∅ primaries with no neutral can be connected in an 2 wire Open wye and the secondaries connected open delta? That is what I was picturing I did not know it was called Open wye/open delta.
In that case the primary neutral connection floats?
And the a secondary center tap neutral can be grounded to stabilize load side voltage to ground and feed some 120V loads?