Solid Roller & Hydraulic Roller Cam Issues

Im in the process of trading my 1997 GT for a 1987 5.0 coupe. The owner of the car put in a solid roller cam without any modifications instead of the hydraulic roller. Now he says it has a miss. If i were to put back a hydraulic roller cam, do you guys think it will run right?....Or is there a possibility that he damaged something in the valvetrain? Thanks in advance