Early 90's means it was probably a K since they started in 1987 so it likely has the Cummins 390 since they started those back with the 580E. I think they stopped using the 188 with the 580B in the 70's. My 1980 580 C has a 207 that still runs good, too, but doesn't have the grapes that the K with the Cummins and turbo has.