One thing new builders seem to overlook , is drawing center lines to line up the parts on center. to compromise the slight off center of the r/r entrance hole , perhaps you could cheat the center line for the entrance thimble a slight amount toward the actual center position , and see what it looks like. On some barn guns , no entrance thimble was used. See how it looks w/ the entrance thimble and w/o the entrance thimble. All it might take is a little judicial stock shaping to fix the r/r entrance position........oldwood