If I install an electric fuel pump in my "56 Montclair, can I leave the manual fuel pump in place and simply
bypass it? My manual fuel pump is "two parts"...it provides vacuum to somewhere.
Thanks.

 

Hello, Tommy, and welcome to the Mercury Forums --
Your '56 Montclair has a mechanical fuel pump that also provides the proper vacuum source for the Windshield Wipers.
If you install an Electric Fuel Pump, you would have to tap into straight Intake Manifold Vacuum, and the Wipers won't work properly.
Manifold Vacuum is erratic, and causes the wipers to slow down or STOP when accelerating. You don't want that !
An electric fuel pump will require a Fuel Pressure Regulator (at additional expense) to make the carb work properly, so is to be avoided.
I would replace the mechanical pump with a quality OEM type. Just remove the old pump, and swap in the new pump. Easy-Peasey.
RockAuto.com has the correct part -- CARTER M73066 -- comes with the gasket. Not cheap, but well worth the cost for the very best fuel pump available for your '56 Montclair -- AND it will deliver the correct fuel pressure while keeping your windshield wipers working properly, and safely.
Carter fuel pumps and carbs have been an industry standard for decades -- really good stuff !
The very popular Edelbrock 4-Barrel Carb is a Carter design -- the old Carter "AFB".

'95 MERC Engine Bay