Fuel pump size??

[BigBlockOlds]

Trying to determine what size pump I need for my 455 build and need a little help.
It will be a long rod 455 (offset ground 425 crank, 7.100" BBC rods) with multiport fuel injection going into my 1987 Cutlass. I have a Buick GN gas tank with a Walbro 255LPH intake pump.

My question is whether or not this pump will be able to supply a 550-600HP engine? I've read conflicting information on this pump and it has me a bit confused. One source says that you need 110GPH to support 600-650HP (the Walbro is around 67GPH) while another source says that the Walbro pump is capable of supporting up to 750HP @60psi.

Does anyone have any insight into this? I was hoping to use the stock tank and in-tank electric fuel pump for ease of plumbing. Is there a larger in-tank fuel pump for this application?

Thanks!