Got it all installed....it took me longer to get the tools together than it did for the installation. Before I started taking anything apart I found out I didn't have a 1 3/8" socket that would fit the heater. No room for channel lock pliers or an adjustable wrench so it was off to NAPA. They didn't have a 1 3/8" in 1/2" drive, only 3/4" drive and of course no adapters in stock. But, they had a 36mm impact socket that fit with just a hair of play in it so I bought that.
Back home, clean drain pan under the tractor to catch any leaking coolant and put the hex socket to it. (I found the plug just to the rear of the oil filter in case anyone is going to do this on a 32 hp Kubota 4cyl) Someone here or on Orange Tractor Talk recommended having having the heater ready to go with the sealant on the threads so it was a quick swap. As soon as I pulled the hex head plug I put the heater right in, only lost about a cup or so of coolant, but it went into the clean bucket to reuse. I tightened it down as much as I felt comfortable with. The heater is brass so if anything was going to give it would be the threads on that rather than the engine block. Got it nice and snug and wiped off all the excess sealant that squeezed out. Installed the plug, zipped tied, replaced the coolant and it looks like I'm ready to go.
Thanks for all the advice guys, I appreciate it. This site is the best!