(I intended to reply sooner, and indeed have had this reply prepared for some days now, but the system would not accept my reply before now, which I have only just been made aware was because I am apparently not allowed to link directly to eBay listings.)
Dennis, thanks again for your reply, I appreciate your insight.
I keep my eye on 3.5F listings on eBay waiting for "my" one to come along.
Here are a few current listings just in relation to lens caps. I'm not sure if there is a pattern here:
eBay item 370778403075
3.5F pre 220 film option, S/N: 2282454, metal cap
eBay item 111004238361
3.5F post removal of film plane glass feature, S/N: 2831693, plastic cap
eBay item 190758790760
3.5F post removal of film plane glass feature, S/N: 2831751, plastic cap
eBay item 350660141543
3.5F white face, S/N: 2852354, metal cap
The thing is, ideally I'd like to get a later 3.5F after the film plane glass feature was removed, but I don't want to get a white face model - I prefer the look of the older face. As I mentioned above, I was hoping to get one that included the original lens cap, and I'm really just wondering if models that fit my requirements possibly only came with plastic lens caps. I prefer the look of the chrome cap, but I'd like to keep my kit authentic and not use a mismatched cap (even if of course it makes no difference practically and fitwise!)
As for my reference book, I'm attaching a scan here of its listing of relevant lens caps. You can see that the plastic cap that is listed as having been "supplied for" the 3.5F was indeed a hinged one, and that there was also a plastic slip-on cap with the same bayonet/lens separation measurements, but which is listed as having been supplied for the Rollei Magic I and II. (The book uses its own numbering system to match accessories to cameras - #15 is the 2.8A, #29 is the 3.5F with factory designation K.4D/K.4E, #35 is the 3.5F with factory designation K.4F, #37 is the 3.5E3, and #34 and #39 are the Rollei Magic I and II respectively.)