First Antipodal Process    (25 q, 20 q)
UR13 = U2 R1 U3 R2 U3 R2 U3 R1 U2 R3 U1 R3 U3 R1 U1 R2 U1 R3 U1 R3

Also....      UR13 ^ 2 = I

Using current techniques, this required a run of about 11 hours.

It remains to be seen how the Kociemba algorithm resolves this
position, and I will try this next.

You mean: F2 U3 D2 L3 D3 R1 U2 B2 R1 B2 R3 D1 L1 D3 R2 U1 D3 (or rather
its inverse)?  Took Kociemba's algorithm 10 minutes.  I do not yet
know whether this is minimal.