After a little research online, read how it's much easier to counter-sink access plate holes and fill with "oops rivets". With the shallow head and 100 degree factory head, there is no need to countersink or dimple the plate-nut itself. Worked outstanding!!
Now must figure a way to rivet remaining two plate-nuts. Was able to access four of them with the squeezer using two different yokes. Believe I'll try back-riveting tomorrow evening. Noticed some stiffener rivets right next to where I'll be working, so back-riveting should work fine. I'll probably use the bucking bar as the back-plate due to the slight offset between the mounting plate and the elevator skin.
Good progress tonight. Happy with that!
Riveting Plate-Nuts
Plate Nuts Installed (minus 2)
Underside: Some rivets to touch up and some to back-rivet still
