Has the engine been run at all, even for a few minutes, since the rebuild?
I'd change the oil/filter first, then prime the oiling system. (Remove the distributor after carefully marking how it's oriented/pointed, take a beefy reversible drill with a long cut-off flat blade screw driver or other similar bit, spin the oil pump shaft counter clockwise for several minutes, re-install distributor). Might be a good idea also to go ahead and change the coolant. Inspect/feel all hoses, especially any sections of rubber fuel line, for any sign of brittleness or cracking and replace as needed. I'd also be tempted to drop the fuel tank and empty it, which would also be a good time to pull the sending unit and inspect the "sock", maybe take it up to a high pressure car wash with some degreaser and clean out the tank. Disconnect the fuel line at the carb and blow out with compressed air, replace any inline fuel filters. When you fire it for the first time, have a few helpers observing to watch for any leaks anywhere in the fuel system or cooling system.
Congrats! We need photos...