It's actually not that bad doing it in the car. I suggest you take the front seat out to aid in having enough room to lie down etc. Having several trouble lights to make it easier to see things will help tremendously.
Be prepared to drop the steering column a bit - use a strong bit of string to "hang" it up from the rear view mirror mount. There will be a cover on where the column bolts to the dash - remove that and you'll see the bolts that the column is held on by.
Disconnect the battery if you haven't done so already.
The 3 connectors that form the bulkhead assembly (where all the wiring enters the car) is easily dealt with if you push the spring clips on the sides of the connector under the dash and allow the whole shebang to come into the engine bay. Then you can carefully disconnect the 3 harness connectors. Don't worry, they can ONLY go back on their proper places as they're indexed.
Go slowly and label everything. Take pictures as you go.
Start on the driver side and work your way across. Remove the various bezels and panels on the front of the dash if they're accessible that way, to allow you to get to things you can disconnect from in front. Remember, if things seem like they don't want to move, don't force things. Also, the harness is held in place by various sheet metal loops that the harness tucks into, so sometimes it will restrict movement of components.
Did I mention - take pictures as you go.
Be gentle - things have been in there for 50 years or more.
Everything disconnects - nothing is "hardwired", so just be patient and diligent. If connectors seem stiff and hard to unclip, sometimes they can benefit from a gentle application of a little heat to make them more flexible - I'm talking about a hair dryer kind of heat... a minute or so will soften up a brittle connector and allow those pesky tabs to be able to be flexed up and over the nubs... don't force things, as that's when they break.
Also, this is a fantastic time to do the MAD conversion and bypass all those nasty high amperage connections that run through the bulkhead connectors.
Good luck!