The hot-start problem ended up being caused by the engine running too hot. It got that way because it was running too fast at wide open throttle (over revving). While mowing with the engine under load it was not as noticeable as when I ran it as part of my testing specifically to get it to the no-start condition. After adjusting the governor and ensuring that all the carb linkage could run it's full length, the engine now runs slightly slower at wide open throttle. In turn, it does not get quite as hot after it has been running for a while and now reliably re-starts even when hot. In the end, I no longer automatically think that this was always a problem with the donor engine. When I moved the Kawi engine from the donor chassis to the burned chassis I obviously had to disconnect and re-connect everything. I was very careful about the cables but did not pay much attention to the mounting bracket. Part of the fix was moving the bracket a bit lower. See pic.
For anyone who thinks it would be cheaper to buy a new one, let me tell you that you are wrong (at least in pure dollars sense). Grossed up I have a little under $2000 total and that includes every thing (even the sand for sandblasting). However, I have sold some parts (even from the burned engine). I am net now around $1600. If I can sell everything that I want, the total cost will be about $1200 - $1400. This does not even count the value of parts that I now have and intend to keep. A new engine alone for this mower is over $2000 at the dealer. An entire new mower is over $8,000 at the dealer.
Now there are those who will tell me that I should count my time. I viewed my time spent on this as leisure time. I do not have a landscaping business. I work on motorcycles (my own) and decided to try my hand at a zero turn mower. I learned a lot, enjoyed it and would do it again. Sure there was some frustration but without that you cannot experience the joy of figuring something out and making it work!
Also, I know my limits. In deference to herler, I have mounted motorcycle tires, trailer tires, and lawn mower tires with hand tools (tire spoons). No way though that I would try that with a car tire. Anyone who followed this thread knows that I brought another SCAG mower because I knew that this was going to be a labor of love that would take a long time. I was prepared to work on this for years buying parts piecemeal on ebay if that is what it took. Only reason it took months instead of years was because I lucked out and found the wrecked mower that had almost all the parts I needed. Going into this, I was prepared to walk away and harvest all the parts I could and sell them and scrap the rest if it did not work out.
Anyway, enough ranting. I did what I did, am happy I did it, and would do it again!