Reggie,
I followed your advice and found this site http://home.provide.net/~cfh/gibson.html

Here are the answers to my questions in case anyone else is interested:

1.-When did the pick-guard change from teardrop to large style?
    A-Larger pick-guard in 1955. The pick-guard became thicker in 1963.
2.-What years did these guitars have plastic bridges?
    A-Plastic bridge introduced in 1962
3.-Did they ever have the adjustable bridges?
    A-Rosewood adj. bridge in 1966
4.-What year did they stop using the banner headstock?
    A-Banner discontinued in 1946 (There waa LG1 in The Twelfth Fret in Toronto with a banner headstock on May 3,2010.)