Engine is pulled - 273 rebuild or replacement 360 crate?

A casting date of 11-5-65 already puts it well into the 1966 model year, so it's not your original block anyway.
It most likely isn't going to take another overbore either.
If you go with the 360 or a late 318, there will be other considerations to deal with (crank pocket, motor mount brackets, etc.)
Just don't make the mistake of tossing the 273 until you have the new motor installed- you'll need parts from it to make the new engine fit (timing chain cover and timing tab, water pump, accessory brackets and pullies, linkages, etc. Maybe the oil pan/pickup/dipstick & tube if you go with a 318 or 273).