It is easy to cut the hole, measure a couple times, cut a small hole, confirm things then enlarge to the 14"x14" opening. The wire is usually taped or coiled up inside the ceiling and the location was figured by airstream to correctly balance the added weight. Post what you get, Andy gave me measurements on our 69 tradewind and the wire was within an inch of his measurement inside the ceiling coiled up and taped to the skin. The other end of that wire should be near, behind or in the circuit breaker area but not hooked up.
On the 62, I don't think there was wiring installed for a/c at least there wasn't on our 63. The power up there might handle it, but you'd want to check what all is on that circuit and figure your wire guage etc. It really isn't that difficult to fish wires depending on where you're ending up putting it, but I'd confirm what the correct location is.