What oil is he using in it?
My experience is that using any multigrade in a sidevalve Briggs will always increase oil consumption, over monograde SAE30.
As far as worn parts go, as you say valve guides and rings are the obvious suspects. It wouldn't be worthwhile replacing guides, or doing a cylinder rebore, on an older Briggs. Even doing the rings might be a toss-up.
Something we used to find with older Briggs, was that lack of servicing of the foam air cleaner would make them run very rich, and that would chop out rings quite quickly. A quick fix for the alloy bore models used to be fitting of a 'chrome ring set', which would seal OK with a small amount [<0.005"] of bore wear.
