Well, since we really don't know what your truck is, its kind of hard to help much. Mopar has been making fuel injected Rams since 1988.

You probably can put a carb and a dist in it. Might be expensive, and wouldn't make any difference on a bad alt or the old battery. Old batteries and old charging systems have been failing since they were first used, being fuel injected has little bearing on that.

If its working now, just drive the truck. Expecting it to screw up is just asking for trouble, and at some point you will be rewarded for your worries. Your truck is a piece of machinery. It needs to be kept up and they can fail from time to time, its part of using them. Gene