The clock blockoff will have the connector for the clock attached to the backside of it and should have 12V power, but one will be when ignition is on and one will be constant IIRC, I might have to dig up some schematics and get back to you.
It's very easy to tap into the fuse block under the dash with a female spade connector. There is even a pin under there for constant power. I'll get links up for it later today.
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