Welcome back to the hobby!

I have both those engines. If I were in your situation I would see if the cranks turn freely and see if the carbs rotate freely. If not then I would free them up by dousing them with glow fuel and try to work them free. I would take the rear cover off the AX engines and look at the bearings to look for rust or damage. I would turn the cranks and feel for roughness, again looking for bad bearings. If the bearings are bad then your will need to replace them (not difficult and not expensive). I would not disassemble the engines further unless necessary.

Cleaning the outside is not necessary unless they are really gunked up, or you just want to have nice looking engines for cosmetic reasons.

If you search on "crockpot and antifreeze" on this forum you will find a ton of information. That method works really well.