Have to agree with XB here....The site would exist, BTW, but with fewer ruined bikes. Too many mods are just not really, say, "well engineered?"
Good upgrades are O.K., but some people end up with beautiful, unridable, or non-running bikes. If it is a family heirloom, why would you want to abuse it? Ride it gentle, have fun....
Remember, if you improve the forks, the frame is not stronger, so that will need to be improved. Many of these old bikes do not have the frame strength and engine that would warrant modern forks and suspension. Modern bikes use stiffer frames to handle the more compliant forks. the frames were originally designed to flex to absorb some of the pounding. When making majoer suspension changes, you often unbalance the bike. A strong fork on a weak frame rarely helps matters.