Russ Here's an easy way.
Make sure all is ready for assembly, shims chosen as necessary, all internals nice and clean and lightly lubricated. The shim thickness bridges any gap between the top of the top bush and the underside of the circlip. A gap will allow the bush to move up and down in the slider. It's not a super critical part, at a push make your own from any hard easily worked material, even ABS or polypropylene.
Assemble the bare stanchion into the yokes and tighten the lower yoke clamp bolt. Feed the new oilseal holders, with the seals fitted, on from the bottom, followed by the circlip, shims as required and top bush. Add the lower bush, washer and nut, and tighten the nut with the leg held firmly by the yoke clamp. Then all off again to add the slider, locate the circlip and tighten down the oilseal holder.
The next stage involves adding the spring, and passing the extended stanchion up through the lower yoke and fork shroud. You will need some way of pulling the stanchion from the top. The pesky little devil invariably wants to slide down just when its almost home.
Proven methods include the official workshop tool, a fork top nut turned down with a length of bar tacked on, or like most backyard fixes, a length of wooden dowel or broom handle screwed into the top of the stanchion.
A later part from an A65 from 1966 can be used as a circlip cum shim assembly. It is a collapsible spacer, a cheap tin can pressing. Part number 68 5134. Described as a Top Bush Widget, to add confusion for want of a simple description. Here in the UK, Drags have excellent stock levels, and at £10 each........
Swarfy.