I have a dodge adventurer 200 (3/4 ton) and want to convert it to a 4x4. Can anyone tell me if dodge used the same frame in the 2x4 and 4x4 trucks that year (1979)??????

NO!
You have to change the center K frame out. Front drive axle hits K frame, but you can take this part of the frame out and replace it with 4WD "K member" parts!