Though I'd chuck both sets of suspension in the bin that is an absolutely classic FSR Comp in original condition so I could understand if you wanted to keep it like it is. If, however, you did want to take that Coupe Deluxe and shove it up Mr Rockshox's fundamental orifice for making such a...
Do you have these foot nuts? You need a 15mm socket and an extension to get them on (or off). I think the z3.5 only had 80mm of travel so they should look similar to these z4s.
The reason you can't find any info on them is probably because they were OEM only forks for the first gen Specialized P3. I doubt very much there are any spare parts for these specific forks out there but I do see them come up for sale every now and then so you might be able to Frankenstein some.
I've got one of those Sunshine big (50T) cassettes on one of my bikes. Thought I was getting a Sunrace as part of a group set but concede I may not have checked what I was getting thoroughly enough. It's lasted well (2 years) and shifts decently. Me no complain.
20mm t/a preferred but 15 mm acceptable.
Fox, Marzocchi or Rockshox ideally
Travel will be 120-150 mm ideally
Must be willing to post internationally.
In the range of 200GBP possibly more depending on the fork.
Love to see what's out there. Thanks for looking.