Distributor seems to jump out of timing?

Mopar Distributor Shaft Lengths
Mopar Distributor identification guide by measuring shaft length, measured from mounting surface to lower end of distributor shaft.

Mopar LA engine – 3.875”
Mopar B engine – 3.5″
Mopar RB engine – 4″
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Chrysler 331/354 Hemi – 4.25″
Chrysler 392 Hemi – 4.5″