Huzzah!
My fuse and MOV came in a few days ago, so I installed the MOV and rigged the fuse in an old car audio fuse holder till the fuse holder comes in from china.
I got everything wired up to test. Double checked the connections, triple checked the ground and verified no shorts. Since I only have a 6 circuit breaker box, I wired one element direct to the generator and the other three to the breaker box. Cranked up the generator and let the engine warm up a bit. Turned on the water, verified no air pockets. May seem a bit silly, and maybe it offered me no additional protection, but I stood on a plastic foot stool to close the output breaker.
Test 1: 1 x 4,500 watt, barely registered on the % meter, brought it up under 25%, with barely a hint from the engine. Volts and frequency holding steady, verified from the convenience outlet.
Test 2: 2 x 4,500 watt. Brought the % meter up to about 65%, engine doing well, volts and frequency steady.
Test 3: 2 x 4,500 & 1 x 3,000 watt. % meter about 95%, engine doing well, a bit more particulates raining down, volts steady, frequency down about 1hz
Test 4: 3 x 4,500 & 1 x 3,000 watt. % meter to 125%, engine showing strain, exhaust noticeably thicker, volts steady, frequency down about 2hz. I let it run here for about 15 minutes and observed the frequency slowly declining. I was able to adjust the frequency back to ~60hz, but it would slowly go down again. Once I opened the output, frequency jumped back up to ~63hz. I'm speculating that as the generator output ran overload, the heat in the windings increased the resistance. Since the load stayed the same, the increased resistance creates additional magnetic resistance in the generator which is transferred to the engine as increase mechanical load, resulting in the engine slowing a bit. An automatic throttle adjuster would solve this. I also observed that the % meter climbed a bit over time.
Test 5: 2 x 4,500 & 1 x 3,000 watt. I let it run here for about an hour. The exhaust smoke cleared up some, I noticed some smoke coming from around the generator and not the exhaust. The temp was just below 240 during test 4, and I noticed that the overflow bottle was low, i.e. low on coolant. The coolant overtemp light did not come on, and there was no indication of running poorly. After shutdown, I checked inside and the smoke appeared to be coming from the exhaust manifold, or roughly the middle top of the engine, and from the muffler or muffler cover. I'm hoping this was just a result of burning off years of dust. There was no distinct smell to the smoke, such as I would expect from burning oil or wires.
Overall, sans smoke at the end, I call it a success. The load bank worked, the generator ran great, all the gauges worked, no complaints. If I had it to do over, though, I would have laid out the elements in a row, like an inline 4 instead of the flat 4 style, it would make the electrical easier to hookup and keep tidy, as well as keep the water connections on one side and the electrical on the other. There were no issues with this, but I think it would be a better design even if a bit larger. As an aside, the water was not really heated on the output, rather it was only lukewarm, I don't think I could use this to effectively heat the pool.
More to come once I get the fuse holder and meters in.