I did the swap so I figured I'd help other people out who are considering this.
The original low pressure line coming from the tank is approx. 1/2 " this connects to a large 1/2" fuel hose that runs along the top of the tank down to the fuel pump which has a large 1/2" input. After the high pressure pump the hoses and lines are all the smaller 1/4" - 5/16"... or 6mm (whatever floats your boat).
What could be a better option would be to nest a normal bit of fuel line with a 1/4" size into the 1/2" tube of the pump assembly. Use submersible fuel line and band clamps to connect the Walbro to the newly placed hard line. Then run standard fuel line out to the stock fuel filter position under the car. Better yet, just connect that line to the hard line and mount the fuel filter under the hood? This would bypass all the fancy bends and having to get under the car to do the filter.
I'll add another post outlining the external pump delete.
Hope this helps someone!