Where to start on my 63 Dart?

Definitely not the original engine. It's a later block with 5 core plugs. Look under the spark plug boot and see if there's a sheet metal tube in there; that'll give you an idea of the age of the cylinder head. It's a bit of a mishmash of parts, though. The valve cover and PCV system is original (and never had a hose going to the air cleaner), but the air cleaner has been swapped for a later design. The exhaust manifold is are later design, as distinguished by their round counterweight, but the intake manifold is from the same era as your car (no EGR fitting). Most of the electronics look like they're the original style.