OBS Fuel Tank - Sending Unit Opening

My '89 Chevy RCLB still has the stock fuel tank. I will be swapping in a 6.0L LQ4 with a single turbo. RWHP is intended to to be 600+. Please pardon my laziness, folks, but the truck is still together and I currently do not have a place to pull the bed off to check the size of the fuel sending unit opening. Dropping the tank is a last resort, so hopefully some wise OBS Jedi will know if the opening is large enough (3.5in+ I.D.) to permit the usage of dual Walbro 255lph pumps.

Detailed forum and internet searches for this information have proved ineffective; any insight will be appreciated.

Pretty sure dual pumps will not fit through the opening in the tank. Just put a single Deatschwerks 300 pump in and call it a day..