Do I NEED to prime it?

If you can get the timing right on and fuel in the carb bowls so the motor will fire and keep running the first time you turn the key, no need to pre oil since all the assembly lube will insure against a dry start.

However, do something a little dumb because you are anxious to get things running can have consequences. For example, during the startup of my first small block rebuild I did not index the slot of the distributor correctly so that when setting the initial timing, the vacuum advance was bumping into the firewall and limiting the advance I could set up.

I cranked and cranked. Finally, I found a way to get it running. Wiped a lobe off the camshaft in the process.