A guy at R3V said that this was a direct replacement for our in tank pump, except that it’s high pressure. The discussion was re. early model fuel pump systems. Remove the in-tank pump and put this one in. Then remove the OEM high pressure pump.
I just did that very thing. I installed a Holley Hydromat , removed the in tank pump and installed the Walbro 255 above the fuel filter in place of the high pressure pump. It runs fine, but I have not driven it yet. Hope to do so this weekend.