I second Jeff's recommedation for Boge turbo-gas cartridges - I just
installed them & they're a real improvement.
I managed to remove the aforementioned cap, with the strut installed in
the car, by using a big pair of channel-locks and putting them between
the coils of the spring, having pushed the rubber boot up out of the way.
Wasn't too hard. Not having to take the strut out is a big win, IMHO.
The only other snag is holding the new strut to stop it rotating while
tightening the lock nut on top - you need some kind of big allen wrench
and a wrench for the nut, and they tend to get in each others way. Still not
convinced I got enough torque on there, but I keep checking it, and it seems
to be staying tight.