Small Engines (Lawn Mowers, etc.): Engine Swap, crank shaft, shaft size

Question
I have an old riding mower.  The problem I'm having is the drive pulleys are diferent.  The old was a 10hp b&s (Model#1707-0139).  The newer one is a 12hp b&s (model# 28-1707)  They mount the same, every thing same except the crank shaft size and pulley.  Do I have to customer make a pulley to make this work or can I buy one for the swap to the bigger shaft 12hp?  Any help would be appriciated.
Thanks
Brian

Answer
You can buy one...trouble is finding one that will work.  

You will need to measure the old stack pulley and then hit the net searching.  Rotary, Silver Streak, and Stens are large aftermarket companies that sell stack pulleys.

You can also try bearing supply warehouses as they often have a large selection of pulleys.  

Ebay is another option or you can look around at you local mower parts stores as they may have something used or new in stock that may work.

Eric