The L6 uses 2 alternator brackets: Lower (2) bolts into left side of block and mounts 5" or 6" (3/8"?) long bolt (going fore & aft) for alternator to pivot on.
Upper bracket is curved approx 6" stand off, bolts onto front of head thru one of the water pump bolt holes and secures upper 1/2" alternator bolt at right fan belt tension.
As far as the 292 P/S option, the power steering bracket bolts onto the head and sides of the block, the lower part has a slotted bracket for the upper alternator stand off. 292 P/S brackets are unique and rare.
The Armstrong version alternator brackets are a lot more common and should be an easy junk yard find. I think 250s and 292s are the same in this respect, but I never ran a 250. Also I've only ever run the stock delcotrons w/ ext regulator, not sure if the "one wire" has the same dimensions.

Every 25 years I like to rebuild that 292 just for GP