Mensan is correct, you CANT use a walbro pump, it will fail (and have horrible driveability, being a gear pump vs a turbine pump). Either go 03' cobra pumps and tank if you plan on making 400+rwhp, or get a BAP and install it to run full voltage ALL the time, BEFORE the FPDM, that way the EEC is still in control of the pumps but can feed the pumps 18.7v if it is needed to maintain pressure @ 100% duty cycle.
The stock pumps wont fail at 18.7v because they arent at it for very long. The walbro pumps WILL fail because they are not meant to be cycled and burn up.
IMHO, get 03 cobra pumps & tank., or just buy a BAP, it takes 2 minutes to install and works.