Bernie Pientka:
John may be on to something. I would be curious to learn how much he had to give to get the unit already re-built. It may have been cheaper than re-building it yourself.
I'm going to e-mail you a search technique which worked for me, but for everyone's benefit, I'm posting what I've learned from living with two (2) re-powers of a spread-frame Cub Cadet.
Understand before you start looking that the single biggest reason small engines fail is lack of oil, period.
First: Make sure to check the condition of the engine by RUNNING it. If it knocks, politely excuse yourself and get out of there as fast as you can; if it smokes at start, I wouldn't worry; if it keeps on smoking, I would worry and start calculating the cost of an immediate rebuild; if it leaks badly (or there is evidence of it leaking badly) be prepared to walk away.
Note: I believe the condition of the BOTTOM end of the engine is more important than the top end.
Second: Make sure you can install it correctly in a Cub Cadet. You're ahead of the game, because you already own a KT-17 so you won't have to buy such things as Exhaust Elbows or "clover-leaf" flywheel-to-drive shaft adapters, etc --if you buy a Kohler. The bolt pattern isn't a big issue, unless you just don't want to drill any more holes in the mounting plate.
<font size="+1">Manufacturer Specific:</font>
For Briggs & Statton Opposed Twin Cylinder 16 HP:
Verify the size of the magnets on the flywheel and the nature of the charging system. I know there were (2) different sizes of magnets installed on this motor, and there may have been three; and at least two (2) different charging systems. The smallest magnets, with a single-lead stator and a half-wave rectifier (a diode) produces 5 amps; the largest magnets with a two-lead HD stator and a full-wave rectifier produces almost 16 amps (I'm working from memory, but I can look it up).
Also, not all engines were made to turn a full 3600 RPM, some of them were designed to power welders and such and turning them faster than designed speed can burn them up. (The engineers at B&S reportedly can tell you what caused the motor to fail and high RPMs is one of the causes.)
For Kohler Opposed Twin Cylinder 18 HP & 20 HP (Magnum Series): Verify whether the engine has a remote oil filter setup, and if it comes with the engine --buying one after-the-fact is relatively expensive.
Please Note: A Magnum can be fitted to a spread-frame without the remote oil filter setup; in fact, it is a lot easier to do, since there really isn't a good place to mount the remote oil filter on a 782 like there is on the earlier MTD tractors on which it was originally installed.
Note: The smallest charging system on the Kohler's equals the biggest on the B&S about 15 amps; the larger, and more common, produces 25 amps and the upsize is dependent entirely on the stator, not the magnets (although you'll pay more for the parts than you do for the B&S).
Honda or other OHV engines: I can't help, I have no experience.
Again, I don't know what John spent for his solution, I paid more than I really wanted to for my motor (I had to buy a working tractor to get the engine, and it was the deck that was worn out, but beggars can't be choosers); but I'll bet I paid less than John. I've been running it for at least 12 months now (edit: 24 months), it doesn't use oil, and just runs better every time I use it. The previous owner reportedly took good care of it and changed the oil regularly. Edit: I never turned a wrench on it except to remove the shrouds (for the first time), lubricate the starter, and glue the magnets back down (after running it for a year with them loose).
I recently came across a Magnum 18 that had come out of a Cub Cadet (the owner upgraded to a diesel) for half what I paid for the tractor; and I don't have to buy all the parts to make it fit a Cub (although I did have to purchase a remote oil filter setup).
Good luck, and keep us informed of your progress.
Just a word of warning though, Donald Tanner can testify that you don't want to post about any "finds" until you have them in your possession.