You're right about the dropped axle requiring tie tod mods, and probably pitman and steering arm mods but your old tie rods are probably in need of replacing anyway and the other mods are simple enough for the average 'bolter to do.

Mono's shouldn't need any other mods, they won't get you as low as a dropped axle and will ride a little harsh. Most all the vendors carry them. Speedway carries Posie's 2-leaf lowering springs that should work good. I'd try those.

You should be able to run your rear axle above the springs. I ran a Firebird rear end that way in a '59 I had. Just check the available clearance between the axle and the frame.

With all due respect to Eaton, monos have been around a long time and were even used as factory equipment on some models. I always take info from someone wanting to sell me something with a grain of salt.