Yep. . . Just answered my own question a second before you posted, Hank. It's a no-go.
Well, I guess I got a spare 3rd gen posi if I ever need one. . . That's $50 down the drain. Oh well, live and learn.
Good news is that the 3rd gen caliper brackets will work perfectly! And even if you factor in the $50 bucks for that 3rd member, I'm still way ahead.