Is it possible to keep old style electronic VR with a dual field alternator?

The main and iginition circuit on '68 and '69 Barracuda will look something like this.
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The dark blue wire ( or dark blue with stripe ) from the firewall connector carries the power when key in run position. The terminal connection at the ballast is used for a junction. A blue (or blue with trace wire) brings power to the regulator. Power for the ignition coil goes through the resistor.

If you have the original harness, then get a Packard 58 - Chrysler type open barrel terminal and crimp like this.
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If you have repop harness with packard 56 terminals, then use a Packard 56. That way you're sure it fits the plastic connector.