Hi Cynric!
Nice find, those look like they will be good working planes for sure.
You could use electrolysis, I did this recently on an old drill press I bought in rather banged up shape, brought it back to life. The electrolysis is easy to do, and it REALLY removes the old rust, and it will loosen any old paint and grim too.
Basically you need a plastic tub, water, baking, or washing soda, a sacrificial piece of steel and a DC power supply. A good car battery charger works for this, or I used an old computer power supply.
You mix the soda into the water (heat up a cup or so of water to make the soda dissolve easier). I think it is 4 tablespoons to one gallon of water (Google "electrolysis old tools rust" and you will find a lot of info).
If you want I can go into more detail, but all I can say is BOY does it work!
The pic is of a part out of the tank, with just a bit of soft nylon brush work done, spiffy clean!
Cheers!