96 was the first year for OBD2. Probably the first year for the crank sensor. The OP's 3.9 will be computerized but still externally balanced. That started back in what 72?
OBDI started in '91 or '92 depending on engine family, they still used a crank sensor and were MPI. Early magnums.
Before that they were TBI ('88ish-'91/2ish?)- no crank sensor on flywheel.
Before that there was a weird quasi computerized carb for a couple of years.
