Have completed it (I think!). Fitting the fork itself was straightforward, it's the attachments that caused my some headscratching. The aftermarket fork that seems to be available is the Paragon Gold TL Disk 65mm.
The Turbo X has 50mm which means the geometry will end up a bit different. The front end is definitely noticeably (and visibly) higher. So after I was done I dropped out the spacers, inverted the stem and tweaked my saddle so that it felt right again. The bike feels amazing to ride - floating on air as it is.
The Paragon fork brace has a screw on the back for mounting mudguards, so that's OK. I managed to also screw the light mount to the mudguard tab which isn't really ideal. I think I would prefer to mount the light onto the handlebars, so I'll try to source a bracket or perhaps one of the super-powerful Supernova lights. [Edit: I found a handlebar clamp for a different sort of light that I have hacked - so now the light is higher up on the bars which is much better for lighting the road ahead and much more stable with the suspension]
To fit the brakes you need a standard brake spacer - luckily I had one lying around. The Paragon's are designed to take a 160mm disk so you need 10mm of spacing.
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The biggest challenge I had was refitting the mudguards, because the mount is completely different. I ended up making some brackets which looks a bit ugly, but works. When I'm happy I'll trim the stays to the proper length. {Edit: done, looks much better]
The the final insult was when I took the bike off the workstand - the kickstand isn't long enough! Turns out that Specialized cuts down the kickstand so I've just ordered a new one with more length.
Total cost: EUR170 for the fork ("Federgabel" in German) + NZD65 for a new stand. A bargain I reckon.