Dating gibson 68 les paul custom reissue
Simply, LSLP have maple tops, whereas 50's examples had solid mahogany bodies.
In fact, a 68 Custom has more in common with a late 50's Les Paul Standard than most people think.
This set of features instantly became the new standard for the Les Paul Custom model, which has been produced continuously by Gibson ever since.
This 1968 Les Paul Custom Reissue was designed to be the final say in historical accuracy, tone and feel.
They have a full nut-width, unlike most 60's Gibsons. Headstock pitch is a shallower 14 degrees instead of the 50's 17 degrees. I need to do some leg work to confirm what an unmolested scheme should be.       Earlier guitars in the run will have a dot over the "i" in Gibson, whereas later guitars will NOT have a dot.       Wired ABR's with no anchors in the wood. :) The ABR's will have a patent number on their bottoms. They have a flat deck where the pickups are mounted just like a 50's guitar.
Later guitars were routed in the traditional 50's style AFTER the maple cap was applied.
(Although, 1950's guitars have a rounded tenon end vs.       They were followed by what I refer to as a “transitional tenon”.
A “transitional tenon” is identical to the “long tenon” other than the fact that it does not extend underneath the neck pickup.
I refer to this mid-1969 through mid/late 70s tenon as transitional because it comes after 11 years production of long tenons and before multiple decades of rocker joints in regular production models.
Guitars actually built earlier in the run (aka, shipped in 68) tend to exhibit routes with straight walls and a flat maple floor.