In general, it is an extremely bad idea to modify your carbs.
Volvo had far better resources, even 30 years ago, to design
all the particulars for your car than you will be able to with
some money and the internet and some tools from sears. This is
why the absolute first thing you should ever do when setting
your car up for maximum performance is to tune it and adjust it
to where the factory intended it many moons ago.

That said, there are often constraints on what volvo did
relative to what you want. Emission laws are one example and
slop from mass production is another. This is why people say
"don't modify the ports in your motor's head but it is okay to
take casting ridges and such off." Volvo didn't bother on the
vast majority of their motors to make them exactly the way they
intended. Cams are another example of compromises volvo made
since they weren't sure if a boy racer or a grandma was going
to buy the 144 when they made it.

So that brings us to this specific situation: High compression
large valve head with crazy cam and twin strombergs. Such a
motor was *never* made by volvo. There is no simple baseline
to use as a starting point for this motor. The best thing to do
is start off with the nearest original volvo motor and hope for
the best through tuning. This likely means B20B with twin
strombs, somewhat lower compression, smaller cam and smaller
valves.

The cam and valves are going to affect the requirements of the
motor at various RPM ranges and loads. Ideally you're going to
put this motor on a dyno with a giant basket of carb parts and
fiddle around until you get maximum torque in the desired RPM
range. You'd do this by swapping around needles and piston
return springs and doing tests between each test. This is what
volvo did to design the motor in the first place.

You can cause the carbs to run richer by making the needle
have a smaller taper. This is how they work in the first place.
Since you've got 2 carbs, you want to modify them in exactly
the same way. Instead of grinding the material off of the whole
radius it is easier to measure exactly how much has been taken
off of a needle by putting a notch in one side of the needle
instead. The needles don't need to be round they just happen
to be so if you make them less round it doesn't hurt anything.
The notch will cause the carb to run richer at a given RPM /
load ratio (ie WOT at 2000 RPM or maybe 3/4th throttle at 2800
RPM).

These things are super complex. Without a dyno and exhaust
gas reader you're simply wasting your time. With a dyno and
exhaust reader you're probably still wasting time...
chris