When I rebuilt my 22r it was out of a 2wd.  I never even thought about the oil pan differences except for the skid plate until it was all bolted in and ready to fire.  I broke it in and drove it a little to check the clearance.  It was pretty tight under flex.  I figured the real test would be to jump it and see if anything hit....I had the other OP pickup and 4wd pan at home so....I did it and the pumpkin just kissed the oil pan where the sump is and left a nice little dent.  Now I have shackles, moved the axle and have rear springs on front, so no more hitting issues.