If you buy an OHV engine to replace a L-Head engine, you will need to buy a muffler also. The Briggs 21**** series engines will replace an L-Head Briggs even if the tank is behind the seat. If you are installing an OHV in the place of an L-Head, you will have to remove the back right post for the muffler to fit on there. The throttle linkage on the new Briggs engines run horizontally instead of vertically, so you may have to get a longer cable for this to work correctly.