I'm calling this 5 hours due to the research involved, but the actual operation didn't take that long. First, I'm a bit frustrated with Whirlwind (again). Figure 3 of their install manual specifically calls out locktite 262 to hold the spinner backplate bolts on. I documented the challenges of finding that particular flavor of locktite in my last prop entry but I did manage to get it. When I went to work on this, I discovered that instead of the AN5-4A bolts called out in figure 3, they used bolts with the heads drilled for safety wire. I emailed Whirlwind and Hector send me back an email saying that Whirlwind now recommends safety wire in that location (just like pretty much everybody else) instead of locktite. So, today I mounted, torqued to 142 in/lbs and safety wired the backplate. Then Kriya and her brother Josh popped down to the hangar and helped me install the prop. Due to the way the lugs stick out of the crank flange , it's possible to mount this in two positions that are clocked 180 degrees out from each other. There is no guidance from Whirlwind on this, nor can I find anything from Lycoming other than the traditional guidance that #1 should be at approx TDC compression stroke when you clock it. It's possible I may have this clocked 180 out, but I wont know until we spin it over a few times, which will happen when I unpickle the engine. Therefore I just snugged the flange bolts up and won't torque or safely them until I'm sure this is clocked right.