Roller lifter camshafts are ground with different profiles than those that are designed to run flat tappets. Having converted a couple of american V8s to roller lifters, I can tell you that it is not a drop in conversion in those engines. I do not know whether there is anyone that makes a roller cam/lifter setup for Volvos. Roller lifters are longer than regular lifters and require some sort of retainer to keep them from rotating. There are some very real benefits from using roller lifters, reduced friction and the ability to use more aggresive cam profiles being the main ones. Maybe someone out there has something that will work in a B20. Good luck,rcs