There were some minor changes to the frame over the years between 1979 and 1982, for instance the shock absorber bracket was changed in 1982. However none of this is major.
The same crossmember supposedly was used for all gearboxes but you may find they do not match or bolt up, a minor issue that many seem to find when swapping gearboxes.
EDIT: Dang, Maverick beat me to it.
BagusJeep lives in Bali.
1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
1951 Willys CJ3A/MB/M38 - Little Willy
1995 Cherokee 4.0 - CHEROKEE