It sounds as though ideally you could use something better. I'm sure many have an opinion of what that might be. You have an early version of that engine. It seemed as though I saw many of these crack, then not for a while and last year a bunch more came to the surface. For others who read this that have this engine, it is standard repair procedure to pop the shroud and at least check these cover bolts when doing maintenance. Kohler suggested pulling the bolts, cleaning and loctiting the offending ones.I would have to look in my notes when, but they did finally make a design change for this year to this engine should you decide to shorty or replace it. If you decided to replace the engine, you would want to be sure it had the new design.

I presume the "crankcase" you reference having a crack is the "big case" and not the crankcase cover (which is directly under the flywheel and Kohler calls a "closure plate").
This is a tough call for me because I try to repair things when they break (or crack) using a few tricks I've learned over the years, but a lot of times things can't be fixed because the overall damage has progressed too far before it makes itself known.
Specifically I am referring to the fact that the crankcase cover itself may be "wallowed out" at the dowel pin holes that align it to the actual crankcase.
If that has happened, the cover may not fit into good enough alignment on the crankcase to afford the kind of match up needed to support the crankshaft evenly as designed.
The only way I would consider trying to salvage an engine in this condition would be if the alignment dowel pins in in the crankcase and their corresponding holes in the cover are completely intact and show no signs of lateral movement or sloppy fit.
A sign of damage as such would be that the cover simply "pops off" after all the fastening bolts are removed, meaning that you do not have to pry the cover apart from the crankcase (as you should have to do if the dowel pins fit properly).
If the dowel pins are sloppy in the cover you could buy a new cover (I'll bet it ain't cheap) but if the dowel pins are sloppy in the crankcase, no hope for ever making it right.
Even if you can reuse the cover (or buy a new one) you still have to deal with that crack. The fact that a crack developed does not bode well for a simple "JB Weld" repair to cure an oil leak. The crack is evidence that a good deal of stress is placed on this area of the case and only a well done Heliarc weld repair will have a chance of fixing that defect.
Good luck to you.
If you decide on upgrading to a different machine I suggest you buy something rated as a "Garden Tractor" instead of a Lawn Tractor (which is what you have now).
By your own admission your intended duties may warrant something beefier than your current machine.

Thanks Fellows, The crack is in the bottom half and runs down at about a 70 degree angle for about 2+ inches. When I crank the engine it spits back through the carb and the engine spins backward like it is firing to soon, the key is not sheared.

I notice the single 20 hp Kohler engine is on a lot of equipment and It seems to have enough power to do the things I need to do, but I am leaning toward something with a little more hp. Do any of you have a suggestion as to what hydro and engine I need? I would like to stay under $3,000 if I can, if not I can go higher if I have to.

Thanks, Larry

I would like to add that I live in an area where it is hard to get good service on anything, I will have to haul a unit at least 25 miles and maybe leave it for 3 weeks.