Huh. You have a mystery to solve. A J20 has a higher GVWR than a J10, notably with a full-floating Dana 60 rear axle. These are always 8-lug, not available in 6-lug. The 6-lug axles the J10 came with are "semi-full-floating" with a flanged axle and a single bearing at the outboard end of each axle.
The sequential serial number part of the VIN is stamped into the right-front-top of the frame. I would compare that with the title VIN, and with the VIN plate.
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Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.