Will watch your thread. Us 273 drivers are getting rarer.
Is this an automatic or manual trans? That makes a difference for model numbers on carb & distributor. I changed to a 4 barrel intake and put an Edelbrock 1403 carb with electric choke on my '65 273, with an automatic trans, in my van and added dual exhaust. I used a small spacer under the carb and a larger, generic air filter, but my van is not factory anyway. Make your car the way you want it, and be practical, is my advice. Remember that high octane fuel is not available anymore. If you plan on building a racer, then costs will be high.
Definitely pull the spark plugs and read them, then time it statically, and check that the vacuum advance will hold a vacuum. With the plugs out, turn the engine over with a socket wrench on the crank shaft and adjust the valves cold. Solid lifter rocker arms need to be watched and adjusted regularly. If the threads on the adjuster bolts or in the rocker arms get loose to where they don't stay put, the valve won't open correctly, and you could get a bent push rod and engine damage. Don't try to run it if it has a bent push rod. Also ensure that the timing chain is not worn out and that it has not slipped a cog. It won't run if that has happened.
There has been some good advice in this thread already. I suggest getting a factory service manual (not just an owner's manual) for your car, if you plan on keeping it. They can be downloaded online.
Best wishes, Richard.