Hi first timer I am getting ready to swap out the rear half of my frame what I don't know is do I need the exact same truck as a donor or are all the rear frames the same

 

Well there were 3 generations of Rangers
1982 to 1992 is consider 1st gen but there were changes in 1989, so that would be gen 1.5, lol
Wheelbase
107.9 in (2,741 mm)
113.9 in (2,893 mm)
125 in (3,175.0 mm)
Length
Standard bed
1983–1988:175.6 in (4,460 mm)
1989–1992:176.5 in (4,483 mm)
Long bed
1983–1988:187.6 in (4,765 mm)
1989–1992:188.5 in (4,788 mm)
Supercab
1983–1988:192.7 in (4,895 mm)
1989–1992:193.6 in (4,917 mm)
Width
1983–1988: 66.9 in (1,699 mm)
1989–1992: 66.8 in (1,697 mm)

2nd Gen, 1993 to 1997
Wheelbase
107.9 in (2,741 mm)
113.9 in (2,893 mm)
125.2 in (3,180 mm)
Length
184.3 in (4,681 mm)
196.3 in (4,986 mm)
198.2 in (5,034 mm)
Width
69.4 in (1,763 mm)

3rd Gen, 1998 to 2012
Wheelbase
111.6 in (2,835 mm)
117.6 in (2,987 mm)
125.9 in (3,198 mm)
Length
188.5 in (4,788 mm)
200.5 in (5,093 mm)
202.9 in (5,154 mm)
Width
70.3 in (1,786 mm)


So if you have a 1998 then you probably need a 1998 and up frame