1964 - 1990 Easy Ids

Easy Ids

Early [pre-68] oil fill tubes had a simple smooth tubular top with a press-on oil fill cap. Late [68-up] oil fill tubes have a twist-on cap with correspondingly enhanced tube shape, AND an engine unit number stamped into the tube, the first digit of which matches the last digit of the year in which that engine hit the streets [well, model year, you know].

A few more differences:
Early:                             Late:
1964 thru 1967                     1968 and up
Big-neck PS pump                   Little 1" or so PS fill hole (1971+)
Early pattern flywheel/flexplate   Late pattern flywheel/flexplate
SB's= 330 CID                      SB's= 260, 350, 307, 403 CID
BB's= 400, 425 CID                 BB's= 400, 455 CID
Block= A, B, D, or E               Block= G, F, Fa
Heads= A thru C                    Heads= C and up
X/W or X/Y xst manifolds           W/Z xst manifolds, if lucky
Forged crankshaft                  Cast crank [99.9%]
45 degree cam required             39 degree cam required
   [except .921" lifter BB's]         [all engines]
No divided exhaust manifolds       May have divided exhaust manifolds

[ Thanks to Chris Witt for this information ]