I haven't, but I've been thinking about how to install a couple Chevy L79 engines, but with only one inlet on the head, I'm not certain how to get full horsepower out of the 327 engines.

More seriously, I've not run into a limitation with my 14 HP Kohler, so I'm good with mine. If I did add a different engine, I would only do it if I could find some other reason aside from power. Fuel flexibility, maybe?

One thing I would think of is getting some flywheel or something, so the RPMs don't drop when running into a pine knot or something.

I have a 15HP Kohler on my LM2000. I wish I had bought the 23HP Briggs originally, but I'm o.k. with the smaller Kohler. It's a good motor with few problems -- a little slower, but it handles everything I put to it.

I got a good price for a 20 hp Honda so I stuck it on my mill to replace the 13 hp.