This is a 289 hydraulic lifter block, I GUESS that means you could use the modern '
oil pressure fed' solid rollers?
That would be my primary concern. Old style solid rollers, those NOT pressure fed, WILL NOT live on the street. Modern roller lifter blocks have taken this all into consideration, can't say that for sure about a 289 block! My old style solid roller cam lost a roller lifter at about 8,000 miles, typical failure time frame is what I learned later.
Anyway flat tappet is cheaper, easier and will last the life of the motor while giving great performance for a 'street' application.