Afraid of wearing out the lobes on a flat tappet? This could be the only real reason I'd consider going roller. One of the main reasons for a roller cam is that you can open and close the valve much faster, because of that roller. Try to do that on a solid and the edge of the lifter would dig into the cam lobe. I might not even bother to have one ground - not sure if its possible but maybe just run roller lifters on an actual 590 cam...
