Small Engines (Lawn Mowers, etc.): replace engine in lawn tractor, craftsman lawn tractor, shaft sizes

Question
I have a 2000 Craftsman lawn tractor model# 917270930, ser.# 050500A004296 and the engine blew up. I'm a mechanic, so I took the engine out, and I wanted to fix it but the parts are hard to come by and expensive. It's a 20hp. Briggs opposed twin model #4617070145E3. Briggs no longer sells this engine, and no one else seems to have one either. My question is this: Will a newer model V-Twin fit in my tractor? The engine I'm interested in is a Briggs model# 40G7770123 professional series engine. It looks like the mounting bolt pattern, and crankshaft dia. and length are the same, but the exhaust pipes are different than the original motor. Does Craftsman make exhaust pipes that will fit, or will I have to fabricate new ones? What do you think of this swap? The mower is still in good shape, and I can get the new motor for $499.

Answer
As long as the footprint is the same, i.e., the engine mounting bolts, and the crankshaft output length, diameter, keyway and threads are the same it will work.  Most of these dimensions are the same across engine manufactures.  This provides more manufactures engine brand and HP options and saves engine manufacturing costs as Briggs, Kohler, Tecumseh only have to machine a few different shaft sizes.

Mufflers will be the most challenging and can be expensive.  However, you can usually bolt headers to the replacement engine and then weld on a muffler.  Throttle controls and very basic wiring may have to be re-routed but should fit if you do a Briggs to Briggs swap.

Did you go to the Briggs wesite and search for Alternator Replacelment or Engine Replacement?\

Eric