Ignore him. He's a Yankee mouthpiece opinion-giver. One of those guys who has no work to show on his own, yet feels that the rest of us are waiting with baited breath for his vaunted opinion. Like...HELL.
Anyway...my history with old Slant's is that despite their mythical status, they don't like high] rpms or low oil when they get elderly.So, may not want to push it too hard until it's time to pull it out.
Be sure you upgrade the rear end and run VERY good driveshaft and U-joints when you get the new engine in.