1 of 2 things happend with the nuts in the frame when the PO had it. The bolts broke when trying to remove them, or the threads were so bad the bolts wouldn't hold. Retapping the nuts with the same size tap won't help if its the latter. The next size up tap could be used to cut new threads.
I saw the same thing happen with a '97 TJ with 137,xxx miles on it. The bottom of the frame was rotten.
1957 WILLYS pickup, needs work.
1973 J 4000,
1978 CJ7 DD.
1979 CJ7 360, TH400/Quadratrac trail Jeep.
1980 CJ5 trail Jeep.
1983 CJ7 pretty weekend and sometimes to work Driver in the summer, My first rebuild, if the Q-trac and 5 are broke, this one is the one to take. its just as capable as the other 2, except nice paint.
1984 Grand Wagoneer, 1 ton axles, great 360/727, and a big a$& tree fell on it .
1989 YJ the CJ to YJ conversion.
2005 TJ Rubicon.
2011 Grand Cherokee Laredo 4x4, Mrs. LUCDOG's DD.
Lots of parts not for sale, i'm a hoarder.