My original is lined, as are the 4 examples of NOS adjustable masts in the pics that follow. 3 are '69's, 1 is a '68, and the 5th mast (at the top, barely visible) is an NOS AM/FM. The '68 mast is exactly .375" shorter in overall length, plus the mount is threaded rather than a splined fit.
These are/were in original GM packaging purchased from GM dealers - 100% positive they are NOS GM.
'69's are 19.375 OAL, '68 is 19.00" OAL. AM/FM fixed mast is 31.500 OAL.