I ended up using manual specified rivets to hold nutplate to forward side of firewall. They are not flat head and hold panel not as flat as I would like. Of course nothing is easy, I tried to drill out and they spun. Oh well, nothing a cut off wheel can't handle. Could have held tail with pliers but Dremil was close at hand. I countersunk and used some flat head aluminum rivets from McMaster.
BTW the manual specified mounting screws for left side of panel are too long.
Y10-01-16