Make sure you flatten all the areas where the bolts are so they are not pulled down.
Use a quality thick cork rubber style gasket and contact cement them to the covers.
Do not and I say again do not use any RTV sealer on the gasket . Install them dry after you glue them to the cover.
This is the method we use and none ever leak.
Not only that we use them over and over when checking valve adjustment. Just don't over tighten them to ruin the gasket. Snug them down with a short 1/4 inch ratchet or small T-bar and go around them a couple times. The Head should be wiped dry with Thinner or reducer as the gasket should also be dry. Any oil between them will promote a leak.
Good luck also use the correct bolts not hardware store bolts with washers. If you need factory bolts I have them. I also have The later style triangle washers. But you can get them off any later engine 85-92 small block.