Simon, could you post some particulars about that guitar? The '61, '62 and early '63 L.P.'s were built on the double cutaway, thin-bodied all mahogany shape that came in late '63 to be known as the SG. Furthermore, that serial number would fit a '64 Gibson or any of the years 1970-1975. If the guitar is the original Les Paul single-cutaway body, it is from the '70's. If it is an SG shape, then one might suppose that it is a '64, but then it should not say 'Les Paul' on the headstock as did the early '60's SG-shaped Les Pauls. The SG-shaped L.P. Custom should have a plastic plate between the fingerboard and the neck pickup with Les Paul Custom engraved. Even rarer would be an SG-like guitar with a pearly block inlay below the tailpiece from 1962.
The '54 RI was introduced in '72 and discontinued in '73. This would be the RI of the original 'fretless wonder' that was introduced in '54. 3 of these were hsipped in '75 and 1 in '77.
Anyway, let us know what guitar we are wondering about, right? That is the only way to come to an understanding of value.