Previous assembly errors were addressed: K1000-08 nut plates were installed instead of -06 nut plates called for in plans; 8-32 screws will be used. One nut plate on left horizontal stabilzer was not riveted correctly. The missed rivet was drilled out; nut plate would not realign properly. Ended up having to drill out the other rivet, realigned the nut plate with a screw and reamed the rivet holes out to #30 for CS4-4 blind rivets. Lightly touched up dimples with countersink before riveting nut plate back in place.