Like George says, the electric pumps will produce more pressure than the SU can handle. Most of them run up to 5-6 psi, and the SU wants no more than 3. If the filter is low in the engine compartment it is fine, so right at the discharge level of the mechanical pump is OK.
The geometry of the float tab that actuates the needle valve is important, and the float must not contact the body throughout its travel.