I would sincerely hope that a PTP Lenco as nice as that would stay together. As with any DIY, you are unlikely to get back the money spent, but that's not the point. You build these things because you can, and because you can generate something unique that can't simply be bought.
I have an L75 in an original plinth, and I fancy doing a PTP conversion. May I be cheeky and ask what I could expect to have to spend? I know you got your slate gratis from an old snooker table, but getting similar from a reclaim yard, or indeed a bit of York stone, wouldn't be beyond the wit of man. Here in Leeds I could get a paving slab for free, they have them literally lying on the pavements, I'll just pick one up.
(Joking, so no outrage please. We do (or did) have stone pavements here but we have had a long standing problem with people turning up in vans with hi-viz jackets and cones and lifting them up, and there are now a good deal fewer about. Add that when repairs are necessary it's easier to pour Tarmac and you can see why a York stone pavement is an endangered species, even in Leeds and Bradford where people still trip over York stone.)