Blade adapter and pulley

I have a John Deere 21 inch walk behind. I decided to put a new engine on it and after I purchased the new engine I realized it has a 7/8 inch crank shaft where my old engine has a 1 inch shaft. What is the best way to go about picking a new blade adapter and self propel pulley for my new engine. Do I purchase these from a lawnmower parts store and if so what do I tell them I need. Any advice will be greatly appreciated.

Don't quote me on it but I was thinking that some of the JD pushmowers were made by Snapper. Snapper has used both 7/8 and 1 inch crankshafts on there products so that could be a starting point. JD may also have the other size.

Simplicity and snapper are Now both made by the Briggs and Stratton corporation.