Alternator question

I'll assume for the moment that you converted the Magnum to an LA style TC/WP and front drive since you are using the same alternator you had on the 273. So, one other thing to consider is that the pulley system you used on the conversion are not the same as your old drive ratios, and may now be underdriving your alternator. Compare your current pulley diameters to your old setup. You may need to use a different (larger) crank pulley or a smaller alt. pulley. These drive systems are best swapped as a complete matched setup.
P.S.- When you swapped engines, you DID make sure to reconnect all of the engine ground straps, right? Good, solid grounds?