I got these nicer used valve covers than my 400 has. Mine were so warped I could never get to seal but these look ok. I've got them all blasted, cleaned, and painted Chrysler blue and I'm ready to install them. I'm using the hard to get Mopar Performance red silicone gaskets. I've got the standard studs and nuts from Year One except I used them all, no screws. I always mess up by not tightening enough or overtightening. I can never tighten a valve cover properly no matter what kinda car it's been. I used the inch-pounds torque wrench last time but it's old and non-reliable. Is there a foolproof way to tighten these now knowing that I'm using used covers with a good straight flange and silicone gaskets? I'm sure its a simple answer but I want to make sure I cover everything so I don't have to change these again for the 4th time before I've even gotten to drive the car.

You dont have a perfectly symmetrical pattern to work with but you crisscross up/down in multiple steps & end up going thru your selected pattern 6 or more times and I have better luck w them ending up being tightened less than what I think they should be (lightly snug) & definitily using your choice of sealer

Use a nut driver to tighten them. That should prevent you from over tightening them .
I also like to use the small little triangle shaped spreader washers to help spread the clamping force out a little.

I use the red high temp sealer on both sides of the gaskets. Finger tighten all of them or in your case lightly tighten. Let set for 1/2 hour, tighten them 3/4 of a turn. Leave them alone.

Well I'm using the MP red silicone gaskets. I don't think they're rubber at all. I sure hope they seal better than those Ultra Seal from MR. Gasket. Of course I was using those on my old valve covers, but still we flattened the old covers and used the copper-silicone and we got one side to not leak but the other was so bad. I just don't want to have to do this again.

Many times the valve cover hangs on the aftermarket runners. Some covers are clearanced on those spots, some are not. Cast covers on SB's are notorious for not sealing as the hang up on these runners. After a little grinding, they sit flush. Use 2 cork gaskets cemented together and you dont have to clearance. Worth checking. 40 inch/lbs or 3.33 ft/lbs is snug at best. Use a nut driver. Can get a way with a little more with a cast cover that doesnt deform.

Cork gaskets are the only ones I use, and the only ones I could ever get to seal. Silicone the gasket on the valve cover side, and snug with a nut driver. Not so much as a seep!

A lot of people overtighten valve covers and oil pans. The nut driver suggestion is a good one. I prefer "glued" the black ultra seal gaskets to the valve cover with Permatex Ultra-seal after straightening the valvecover metal, especially around the holes. I then coat the side that touches the head with a wet coat of motor oil and tighten evenly with a speed wrench taking care not to over tighten. I check the bolts occasionally and keep them snug.

If you are running stock exhaust manifolds, it may be cooking the gasket along the lower rail. I think there was a shield or special gasket made to provide a solution to this?

It isn't rocket science.

I prefer the silicone coated steel shim gaskets, but I have used all the commonly available types.

I have almost never used RTV, a crutch for poor workmanship, imo.

Flat rails, on the cover and head, fresh gaskets and properly torquing to spec is all that is needed. I might use a spray glue to glue the gasket to the valve cover to ease installation, but I have also used thread to tie the gasket to the cover.

If you get into aftermarket intakes or covers then you prefit and check for issues, fix them and install as above.