Regarding the dash mounted clocks, the 1966 and 1967 Coronet models use the same unit, factory part number 2661 816. As far as installing one of them, it's been awhile since I've looked at one, but I believe that it's a three wire set-up, one for power, one for ground and one for the light bulb and socket assembly that plugs into the backside of the clock.
I personally do not know of any companies that are reproducing these clocks, so you will need to find either a used one, or an n.o.s. one. The n.o.s. ones are getting a lot harder to find these days and are fairly expensive if you can find one. I know where one is located now, but the asking price is $275.00 plus shipping from the company that has it listed and they mention that the clock does not include the factory box, so I'm not sure if the installation instructions and other misc parts that came in the clock package are included either.
If you can find a used one somewhere working or not, there is a company that makes a quartz conversion kit for these clocks, so that might be an option also and hopefully much less expensive.
To be honest with you though, unless you absolutely have to have a factory clock, I'd recommend that you just restore the clock hole cover plate that your car has now and spend your money on other more important items. The factory clocks from this era are not very reliable and even with the quartz conversion kit installed, there isn't much guarantee it will continue working well all that long. These older style clocks just aren't nearly as nicely built as the ones we have in our newer vehicles.
Richard
Here is what the factory 1966 and 1967 dash mounted clocks look like (part number 2661 816).
The 1966-1967 clock hole cover is part number 2631 122.