An update: I finally have the clutch installed in the Centurion, or at least in place.
We were held up tracking down a lip seal for the clutch, the one that seals to the crankshaft. It's installed in a crankcase cover that's part of the clutch assembly. You can see it in the first photo. The original seal was 4 15/16" outside diameter. Despite Garlock and Timken making a large selection of inch-size seals (and probably others), they are a bit limited on the 1/16" increments, especially in the larger sizes. So we bought a 5" OD seal and bored the cover out to suit.
With the clutch finally assembled, I then struggled to get it installed with the engine and the transmission in place, the engine loosely, but the transmission fully installed.
What did the trick was supporting the engine in the hull with the gantry crane at a 45 degree angle to the centreline, and unbolting the left-hand fan so it could be pushed back towards the transmission. I then dropped the clutch in beside the engine and finagled it into place.
That was the last major hurdle to getting the tank moving (I hope).
Malcolm
