[Hank70SS]

You don't fill the rad to the top on these cars. About 4" to 5" below the top. You can add an overflow tank but it's not necessary, I don't have one and mine never overflows. If it's the original rad it could be plugged up. Maybe just a flush or maybe it will need a recore.

If your timing is set to stock specs it probably needs to be advanced some. Chevy big blocks love a lot of timing advance. Try setting it to 16* even 18* at idle. Watch for spark knock, it can kill an engine. You may want to start at 14*, if no knock, try 16* then 18*. You'll need a dial back timing light or timing tape around the damper to check total mechanical advance timing. It should be around 35*, 36* and should be all in between 3,000 to 3,500 rpm. Your mechanical advance may not be working well if it's a stock distributor and not been rebuilt in awhile. The above timing checks are done with vacuum advance disconnected and plugged. If you're sitting at stock timing now that 454 will really wake up with more timing advance.

You have a fan shroud, is it a stock clutch fan setup? Fan blades should be about half way into the shroud. Is the clutch good? May be time to replace it.

Check vacuum hoses, make sure they're all good with no cracks. A vacuum leak can cause it to run lean and that will make it run hot.