Special sleeve for the stock deck height Briggs Model 15 block. It has a 1/8" thick shoulder on the top to prevent the sleeve from moving.  Some people will bore the block and leave an aluminum shoulder at the bottom of the cylinder to keep the sleeve from dropping down into the block. The problem with that method is that the aluminum skirt of the piston comes out of the bore when the piston goes all the way down. An aluminum piston rubbing against that aluminum shoulder will tear the heck out of things in no time.

The dimensions of the sleeve:

3.00" ID, 

3.190 OD

.095" wall

3.6" Long

3.290" OD of the sleeve shoulder

1/8" tall shoulder

 I have the stock crank, stroker crank and pistons in stock.