Those old flat tappets were really "slow" lobes compared to now. Valve springs are about 900% better now. Some of the older grinds will rpm with light valves and light retainers, as they did in the day, but they hurt bad for bottom end and mid-range. I would say that cam would struggle to see 600 hp. There are creative ways to control the valves nowadays. Lobe design has come light years, and keeps getting better. CNC cam grinding has eliminated having to make masters just to try new ideas. It's on the screen and keyboard, and then BOOM......new design. We explore stuff now that would have been unaffordable before the CNC cam grinders cam along.
Also, new spring materials, ovate wire, conical and beehive innovation has brought lightweight and effective springs that require less pressure to do their job.
Roller lifters didn't have the pee holes for many years. Pressure fed oil is absolutely better, and required for bushed rollers, but a person can get creative with the cam lobes, valves, valvetrain, and springs, and do things now that really work well. Things that had not been possible until recent years. A severe duty Crower, non HIPPO with less than 600 open pressure can live pretty good in the right set up. No doubt a roller is the OP's best option if there are no rules to prohibit.