93 jeep yj sbc 350 swap with th350 2wd transmission

looking for advice on turning a th350 transmission from 2wd to 4wd. also would like some help with load issues. isntalled new alternator in the process of changing wires out. when under full load (driving heat on wipers going all lights on ect.) my voltage will drop from roughly 13 to 12v or less. in the process of rewiring the alternator with a dummy light to see if that will fix the issue. Just wondering if anyone else has ran into this problem. when i stomp on the gas while in park the voltage gauge will go from 12v to roughly 13v in idle after starting up. Thanks guys!