So far as running just props on your bench, Manly has had very good success doing this for the past few years. They seem to have back rowers that can go the full 80 minutes and they just rotate their props. I know this practice can take a toll at the end of the season on players but we have 80 minute players in Ellis, Fulton and Hino.
My preference is not to see Blair spend the majority (or any) of his time at prop, in fact, I couldn't think of anything worse. I'd like to see him on the other side of the field running the opposite angles Ellis does (like Dwyer was starting to find).
We are at our best when scoring points. Sure our defence has picked up really well the past few years and I think Folkes has to be given credit for that but Blair is an attacking buy in my opinion so use him for that and let the other props (Keith, Woods, Groat, Bell and BMM) do that role.
Have waffled on like I have, I forgot Sheens likes to run a back on the bench....