That must be a body casting number there, not the R list number. R6910 is an 800 cfm on your list and mine.
Here is another reference that is probably correct:
1850-3 Carburetor Info Page
Your spark looks good. That is the right way to check for spark energy. With that spark and a bit of fresh fuel down the carb throat, and ignition timing anywhere near to right, it should have at least sputtered.
So either fuel being bad/not fresh or ignition timing is back on the table. Were the spark plug wires removed in the installation process?
One more thing but not likely: Did you disturb anything on the heads or valvetrain, like rockers or pushrods? If you have a compression tester, then I would check cylinder compressions just to get that question out of the way. If you don't have one, then hold that idea for a while.
