If you don't have a fuel return and the pump flows enough it will keep on pumping fuel into the carb when it doesn't need it. So on idle the float chambers will fill up and fuel will be forced into the barrel.
Interupter pumps flow more and at a higher pressure. They are also larger. They usually need a fuel dampener to.
Solid state are smaller and don't flow as much or as high a pressure.
For carbs you want solid state.
I know webers have the return I am sure dellortos do as well (its been a long time since I saw dellortos) . They must do cos you usually fuel them in series, i.e. fuel in one inlet then out the return intothe other carbs inlet and then out to the tank.
Or a branch feed set up where theres T pieces off to each carb but the returns fitted with a resrictor.
Also make sure the pumps wired up to a cut off. You tend to panic where your upside down in a field with an electric fuel pump buzzing away spraying petrol all over you.
A way I recommend is oil pressure, no pressure means the engines not running so no fuels pumping! Cos its a carb it have float chambers so it will start up no bother.
Anyway you need to find out what the air flow (highest air flow is at peak hp) is then the AFR (or go for 12.5:1 thats sually best for peak power) and work out what flow you need. You should be able to find the recommended pressure for the carbs from somewhere, usually its about 4 - 5 PSI.
I've still got the FPR regulator I used on my twin dellortos. It's a pro-line (??) one. Has has the connectors and some hose on it.
If you want it PM me (can't remember just at the mo hopw much it was though??
my twin delloro's were fed in series.
No return to tank (pipe was blocked off).
Facet red-top pump used to as the pump. - mounted as close to tank as posible - infact where old fuel filter used to live.
Also dug out the garage a head breather that you may find usefull. Basically it's a K&N with a specail plate and the right size pipes to fix to head. - You my want this as you're running carbs so won't have the head breathing back into the inlet manifold.
I've got some pics of both things. I'm just off to pick up a chinky so not got time to upload now. Will do it tomorrow day time - beats the hell out of actually doing some work.