Just to wind up this thread with a conclusion, It was not hard to compress the shock unit to 6 11/16 in. It seemed safer to press on the spring housing directly rather than through the shaft, so I used a 1/2" pipe nipple and a couple of grade 8 washers like this:
Will make sure there is some end play when I put it back together.
Appreciate all the expert guidance on this. Now, the only question in my mind is whether, in the event of a prop strike, the unit will expand back out again….