http://en.wikipedia.org/wiki/Chevrolet_Advance_Design

From Wikipedia

1947 - Gas tank filler neck on passenger side of bed. No vent windows in doors.
Hood side emblems read "Chevrolet" with "Thriftmaster" or "Loadmaster" under it.
Serial numbers: EP 1/2 ton, ER 3/4 ton, & ES 1 ton.

1948 - Transmission shifter now mounted on column instead of floor. Serial
numbers codes: FP 1/2 ton, FR 3/4 ton, & FS 1 ton.

Early 1949 - Gas tank now mounted upright behind seat in cab; filler neck aft
of passenger door handle. New serial number codes: GP 1/2 ton, GR 3/4 ton, & GS 1 ton.

Late 1949 - Hood side emblems no longer read "Thriftmaster" or "Loadmaster", but
are now numbers that designate cargo capacity: 3100 on 1/2 ton, 3600 on 3/4 ton,
3800 on 1 ton. Serial number codes remain the same as on early 1949.

1950 - Telescopic shock absorbers replace lever-action type. Last year for driver's
side cowl vent, its handle is now flat steel, not maroon knob as in previous years.
New serial number codes: HP 1/2 ton, HR 3/4 ton, & HS 1 ton.

1951 - Doors now have vent windows. Mid-year change from 9-board bed to 8 boards
per bed. Last year for 80 MPH speedometer, chrome window handle knobs, and chrome
wiper knob. New serial number codes: JP 1/2 ton, JR 3/4 ton, & JS 1 ton.

1952 - Outer door handles are now push button type as opposed to the previous
turn down style. Speedometer now reads to 90 mph and dashboard trim is painted
instead of chrome. Mid-year, Chevrolet stops using the 3100-3800 designation on
the hood and changes to maroon window and wiper knobs. New serial number codes:
KP 1/2 ton, KR 3/4 ton, & KS 1 ton.

1953 - Last year for the 216 cu straight-six engine. Hood side emblems now only
read 3100, 3600, or 3800 in large print. Door post ID plate now blue with silver
letters (previous models used black with silver letters). Last year to use wooden
blocks as bed supports. New serial number codes: H 1/2 ton, J 3/4 ton, & L 1 ton.

1954 - Only year for significant design changes. Windshield now curved one-piece
glass without center vertical dividing strip. Revised steering wheel. Revised dashboard.
Cargo bed rails, previously angled, now horizontal. Tail lights round instead of
rectangular. Grille changed from five horizontal slats to crossbar design commonly
referred to as a "bull nose" grille, similar to modern Dodge truck grille. Engine
now 253 straight - six. Serial number codes unchanged from 1953. Hydromatic
automatic transmission is available for the first time.

1955 First Series - Identical to the 1954 model year, except redesigned hood-side
emblems and modern open driveshaft in place of enclosed torque tube. Serial number
codes unchanged from 1953 and 1954.