Hi Andy - if you could find a way of showing some pictures, that would be a massive help.
The book you refer to is the Guru's Guitar Guide - that's about all the info on Franconia that's around - and I'm personally not convinced how accurate it is.
I recently had a Franconia Jazz bass copy - it had all the features you'd expect to find on a 70s jazz - maple fretboard & block inlays, thumbrest, ashtray pickup covers, Fender headstock shape etc. However, after owning it for a bit & dismantling it for some light restoration - I don't think it was Japanese. Components, materials, construction & build quality all said 70s Korean to me.
As far as I know, the Kay LP copies you mention were Korean - is yours like the FX Kays, with just a cover plate instead of all the gadgets:
http://www.univox.org/pics/guitars/lp_fx.jpg
I have seen effects-less versions of these - although you're right, these have bolt necks.
As usual with these things, it's all guesswork & speculation - the importer which owned the Franconia name probably sourced guitars from various different factories, as many brands did, so quite likely some of them were Japanese.
Anyway, it sounds like an intriguing guitar, & I do hope you can blag a camera & get some pics up.
Jon.