I ran an external Walbro pump with EFI. The big thing is keeping the restriction from the tank/ sock/ pickup/ tubing TO the pump very very low. If you use a suction filter make darn sure it is oversized, and RATED for suction side service, and has VERY low pressure drop. That is the key, I think.
Make certain your return is at least same size as supply. With my first TBI I made the mistake of using the 1/4" tank evap line for return. The drop in the return was on the border line. When I changed the system to Holley HP that got worse.
