Wow !
Good work Andy, 150% for effort and willingness to experiment! Especially shorting the output - just how many hail-mary's does that take
That 29V a.c supply would be perfect to avoid the difficult current source. With an extra rail available, there is a 'slightly different' schema that could be employed by creating a negative rail - this would have the advantage of being to regulate down to (near) zero volts. i don't know if that is something that would be useful to you ?
dc