Chris:

A plain bearing engine will work fine as a pusher, without excessive wear, so long as you do two things.

First, no plain bearing engine will live long without castor oil. Many of these engines were used as pushers with good engine life in the days before the synthetic oils became predominant.

Second, very few of the older plain bearing engines did not have a steel washer between the prop driver and the front of the crankcase. Many modern plain bearing engines either have a fiber washer there, or no washer at all, leaving two aluminum parts to rub one against the other. A fiber washer, while better than nothing, will wear quickly leaving the two alloy parts rubbing, galling, and destroying themselves.

So. Make sure the engine you have selected either has the steel washer there, or install one. Then, with a goodly percentage of castor in your fuel mix you should have no problem at all.

Bill.