thanks a lot for your answer.
I know, that without the suitable sending unit I can't install the return line.
Mike (from pontiactripower.com) said, that the tripower cars only persist a pressure about 4 psi.
So, when it's getting a little bit warmer outside (here in germany), I'll check this (all).
OK, then you are aware of the return line going to the tank.
Have heard this about the fuel pressure before as another member was having issues as well and believe he had his rebuilt by the same service. I am OK with 4 psi AS LONG AS you have the needed gallons-per-hour (GPH) flow.
Simple example to keep in mind would be 4 psi pumping 40 GPH versus 4 psi pumping only 20 GPH. It is not necessarily the psi alone you need to be concerned with, but rather how much volume the fuel pump can move at that psi. The higher psi can overcome the needle and seat if too excessive, but not enough volume of gas and your carbs will go dry under wide-open-throttle.
This is condensed from a website on fuel pumps, flow, & HP;
"Often the custom shop will advise a fuel pump upgrade, suggesting a fuel pump rated to support as much as 4-6 times engine horsepower. The reason given is the effect acceleration has on filling the float bowl, driving the standing fuel back against the pump, raising head pressure, killing volume, and reducing the gas flow. The fuel systemís first priority is to keep the floats from running low enough to uncover the main jet, running the engine out of fuel. It may not seem significant but the weight of fuel above the main jet does impact fuel flow through it, and therefore the air/fuel ratio of the engine under load. This is critical if engine tune is to be held across the rpm band, achieving peak performance from cruise to hard accelerations. Under hard acceleration the typical fuel delivery system struggles because it must start flow up the line against the G-force developed during this time."
GPH fuel flow can be reduced as much as 50% from restrictions in the fuel system such as a clogged/dirty "sock" on the end of the fuel pick-up tube, fuel filters, bends, rubber line, elbows, heat, 1/4" return lines, etc..