Well after several ideas such as spacer blocks and such, my only other suggestion is to find a dyno shop and get someone that knows Webers and hopefully Porsches with carbs and run the car on the dyno. In southern CA we are very fortunate to have several and ALL the race pre shops use them and as Wayne Baker (#22 car) likes to say: an hour on the dyno is worth a DAY tinkering at the track!

As part of the setup they hook up fuel pressure, ignition sensors and even exhaust temps from each cylinder so everything can be seen and adjustments made. That is what was done on my car every time we had the engine out or at the beginning of every race season.

The issue with fuel is NOT pressure but flow ( gallons per minute) and it is measured by how well the engine handles high power runs and doing this over a 30 minute or 1 hour race session. There are several web sites that let you enter all your engine specs and it gives you what capacity pump is required. This is usually for water cooled engines though and we found that getting a pump with 150% or their recommendation worked very well. I used Holly pumps and the capacity ended up giving a fuel pressure of 6# and the regulator lowered it to 3.5 or so. Note the regulator reduces pressure and should NOT reduce flow and I think the Holley regulator does this well? When the race car was built, the complete stock fuel system was pulled and trashed. We did not use a bottom feed tank, as the fuel cell suction came out the top with a baffle for the pickup. We used 1/2 inch SS solid lines, no return, no filter at pump suction, Porsche 930 filter at the engine compt just before the lines split for each carb, each carb had a small filter, the fuel inlets at each carb was connected to smooth out pulses and surges and that is where the pressure gauge was (not on the filter). We tested capacity yearly as part of the dyno test and if I remember correctly it was about 25 GPH or so. The carbs were rebuilt each year and every two years sent to Pierce Manifolds for a complete redo which is $$$$$$ but they are better than new.

have you ever cleaned or replaced the metal mesh sock/strainer/filter that is on the fuel outlet tube inside the fuel tank? did you remove and flush the tank prior to installing your new engine? have you replaced EVERY inch of fuel line?

"black crud"...deteriorated fuel line? btw, if you are using the the CB/Carter version pump, when you received it there may have been a round metal canister attached. it is a before the pump filter. when i installed the CB pump on my carbed car i took the metal filter off and replaced it with a stock FI filter upstream of the pump.

on p 50 of the cb weber manual. note item #3. a gause filter that is in the fuel inlet housing that is located on what would be the outside of the carbs when installed (1 per each carb). with what appears to be your fuel delivery issues, i would ensure they are clear as well.