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The 1st generation "square" ones from 82-93. Also can use the rear end from the 4x4 S-10 Blazer. The '94 to '04 2nd generation should also be the same width, except for the ZR2 version. They had factory wheel flares and I have to assume the rear ends were wider than a regular 4 x4. You would want to avoid that one.
Thanks, didn't know that. Other GM brands may have discs but not be as wide? I recall seeing Oldsmobile Bravada with 4 wheel discs but don't think it was as wide as a ZR2. FWIW, I put mine under a '54 Chevy. The '48 Fleetmaster OP asks about should be similar?