sanding the carb and cyl bores from no air filter merely hurt the engine compression and silica level... ( minorly )...
white smoke at startup and overheat.. I'd be looking at a head gasket first. checking oil for water.. and water for oil.
if you find water in the oil.. don't run her.. coolant will wipe mains fast.
go from there based on what you find.
there are a variety of tests you can do.. including wet / dry compressiuon.. leakdown tests, pressurized cooling sys test.. and if need be.. pan drop and pressurized cooling system looking for drips.
also read plugs. if one is steam cleaned.. you know you have water in the combustion chamber on that lung..