Dave
I have enjoyed watching this topic with interest, as I did exactly the same job on my ’93 +8 last October.
I did not use any spring compressor at all. I wound down the bottom plate until the rebound spring was de-compressed using threaded rods like you used to reassemble, and then it was easy to remove the old main spring, and simple to install the new Mulberry one, by hand. Nothing scary about it.
Like you I fitted the top of the new pin into its socket before compressing up the spring again, as I reckoned it would be easier to line it all up with only very little compression in the main spring. The method advocated on the GoMog site didn't appeal to me as it would have meant trying to fit the top into its socket with the springs fully compressed.
As for bushing and reaming, I took both stub axles to Macdonald Racing near Durham, and they did the job for me in half an hour while I waited. Cheaper than a reamer, and less hard work!
Keep up the good work!