Another update. I received my Speedseals for the Lehman and my Northern Lights genset. In the process of installing the Speedseal on the Lehman, I pulled the impeller so I could sand off any debris/irregularities on the impeller housing seal face.
Backtracking for a second, the last time I installed the impeller, I wasn't sure if I had got it all the way home. I had not greased the shaft or impeller hub and it was difficult to install. Regardless, it looked like it was 98% of the way in at worst, and the cover sealed properly, so I left it as is.
So going back to this time around, I greased the impeller shaft and hub before reinstalling the impeller, and it popped right in, definitely a mm or two further into the housing than before. I reinstalled the original cover (not the Speedseal, still working out some kinks).
When I fired up the engine, the raw water flow rate out of the exhaust was probably 4x what it was previously; far more than I had ever seen since I acquired the boat. It also ran about five degrees cooler than before, reading about 195F on the gauges at 1800 RPM. It's still warmer than I was used to seeing, but I'll take a five degree drop.
Coolant consumption also appears to be nil.
We're taking off on a week-long trip to the Puget Sound area on Monday. Will be interesting to see how she performs. With everything I'm seeing right now, I'm quite confident that the engine will perform well.