4 spider units usually have the "big" bearing hub on them . To put them in a 3.062 case you use a 603049/603011 bearing set ( #37 in wheel bearing sets). To put one in a "small bearing" case you use the "slim line" bearing set 102949 and 102910 I don't remember the "set" number. IF the posi has the small bearing hub , you will be limited to a small bearing case and the 503049/503011 bearing combination. The actual cases all fit the same housing from 57-78 (or 79 truck).
Randy