I've noticed that some earlier ST's do need to disassemble through the hole at the back. I did fix up a series of thin piano wire rods with a tiny hook on the end, and with this I could fish out the pin. This is after grinding the points (or finding the right pair) on a pair of pliers so fine they would reach in and hoick out the circlip. Or a thin and strong enough pair of tweezers. Then to reassemble, a brass tube of appropriate dia., to hold the circlip in the required dia. to go into its seating, a second tube that fits in the first one to hold it square in the first tube and push it out once it is in place, so it springs out into its seating, and finally a rod through the second tube to centre the whole caboodle in the pin. Hope this makes sense.

John
Dumb question but you have pulled the sleeve out?
Make sure rod can slide on wrist pin to back of piston, old castor goo funk can stop it from sliding back.

On the bearings.
What quality did you get?
You need the best or may suffer ball retainer pieces through the piston/sleeve when parts are slung off retainer.
The Fafnir bearing with phenolic retainer is basically blow proof and what I always used.

What parts are you looking for?

David