So the bike took a trip to C B S Whitton today, fantastic bunch of guys there. Super helpful.
Turns out I'd managed to measure the clearances wrong, so they were all in spec after all... but it's now been looked at so I'm happy! They took a look at the Cam Chain Tensioner as well, and agree that someone has previously over torqued one of the bolts, but as the shims didn't need changing we all agreed that it was best left how it is until it needs to come out!
Also got my chain correctly tensioned (after I fitted a new one last weekend) and adjusted the clutch cable properly. All in all, well worth the money I've paid them... and I'll certainly be going back to them in the future