1990 FWC 454-How often should I flush and replace antifreeze?

If I put approximately 75 to 100 hours on my twin 1990, FWC 454 Crusaders, should I flush and replace the antifreeze every year? I don't want to take any chances messing things up.
Nightstalker

Every two years is what the service interval calls for. In my 1992's I added some of that radiator cleaning crap they use in cars and let it run thru for about 2 hours then flushed the system and re-placed the antifreeze. It really wasn't too bad adn my antifreeze is now 1 season old...looks very clean. I would have liked to try one of those older type Prestone in line flushing hose things ( like back in the 70's ) but I am sure they stopped making them for pollution issues as they basically allowed you to flood the ground with anti-freeze and then water