When I purchased my 68 Les Paul Standard in 1970 it was fitted with a B3 Bigsby and Gibson E340 strings. This was in Brisbane Australia so the strings were possibly factory fitted. From memory the gauges were 13 to 56. The sound of open chords through my Fender Silverface Twin reverb was like an anvil being hit with a hammer. I did have strong fingers but changed to E340L's later, possibly 11 to 56. Using 10 to 52's on my Gibsons now and 10 to 46 on my Fenders. Re caveat: The sizes could be different to what my memory remembers so would appreciate any confirmation or otherwise.