50 weight oil to the fill line (before putting the top on) should not result in much (if any) oil being sucked into the carburetor. An overfilled base and/or lighter oil might allow oil to get get sucked in.
I've used 3 or 4 different sizes of oil bath filters on 216/235/261 one-barrel Rochester carbs over the years with no problems. If water gets inside, you can expect rust-through in the base and maybe deterioration of the filling (you'd also have problems with a paper element if it got wet).
Nonetheless, on the 2-carb (Carter-Weber) set-up that's going on my 261, I'll be using oil-bath cleaners adapted for paper filters (because the base had to be cut to fit the top of the C-W).
