Small Engines (Lawn Mowers, etc.): Engine pulley switcharoo, diameter shaft, toro snowthrower

Question
I have a 1981 Toro Snowthrower 524, Model 38040.  I'm switching the 5HP (worn out) engine with a used 8HP (not as worn out).  Mounting brackets etc., switch over just fine...the only problem seems to be the size of the crankshaft.  The 5hp has about a 1" shaft, the 8hp has 3/4" shaft...I need the 2 slot engine pulley from the old 5hp...but the shaft on the 8hp will not accept it.  Can I find the same size pulley for the smaller shaft of the 8hp?  If so where?  Or should I try welding the pulley with the bigger diameter shaft hole onto the smaller diamer shaft, anticipating never using the 8HP engine for something other than the snowthrower?  I am stumped...please help.

Thank,  Jason

Answer
I bet you can find a correct size pulley but I don't know exactly where.  

I'd hold off welding it as long as possible.  You my be able to find a sleeve adapter.

What do you mean by a 2 slot pulley?   2 belts?

Measure the outside diameter of the pulley and the key way size and I'll check some books.

Let me know about the pulley and it's size.
Eric