I suppose it's possible to wire the dash in the car but
I wouldn't even consider it. It's sooo much easier to see the wire connections when the dash is sitting on a (padded) bench.
Disconnect the steering column clamp connections at the forward end of the footbox and at the dash cross-brace. If you have a glovebox, leave it right in place. If your fresh-air cables are connected, unhook them from the valves.
It's easy.
