Age of 413 timing chain or gear?

[rattlenbang]

I'm replacing the 440 in my Dodge empress with a 413 I stumbled on. This truck originally had a 413, I replaced it with a 440, a friend accidentally trashed the new motor, so I'm back to the 413 again. The original 413 had gear-driven cam, but this one is a chain. I can't find year marks and there is very little on the top pad, just "HT 413" I know at some point they dropped the gear (I have no idea why, gears last longer than chains). Anyone know when? I'd be interested in having an idea how old this engine is.