Blau911;
If you don't mind I'll share my $0.02 based on some calculations that I've done.
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As a result, I am wondering if the primary loss of my low end torque is due to over aggressive cams, or the large increase in porting - or a combo of both.
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* Your Cams: According to my numbers, your 120/104 cams are not a "Hot Street/Mild Race" cam -- at least if you don't consider more lift and duration then a 906 cam to be "Hot Street/Mild Race". Porsche didn't even bother plotting the torque on their 906 spec motors until 4500 RPM and generated peak torque at 5500 RPM and peak HP at 7800-8000 RPM which gives you a clue as to how radical they are. Do you know what the cam lobe separation number is on your cams? If the lobe angle is wide (thus reducing the overlap) it might help a little bit with the low speed performance.
* Your Porting: 38mm is what Porsche used in their full-race 2.5ST's which used the aforementioned 906 cams and rev'd to 8500 RPM. In general all of the carb'd or MFI'd 911 engines that I've checked (which is most of them) had a peak torque intake gas speed 60 to 80 meters per second. This includes the racing models. Your engine's intake ports are larger still at 39mm's. Assuming that your engine also develops its peak torque at about 5500 RPM, your peak intake gas speed is about 56 m/s. Too slow of an intake gas speed can result in the fuel actually dropping out of suspension in the air which will result in poor combustion.
So my answer to your question is YES. Your problem appears to be a result of too wild cams and too large ports. Putting a set of normal S heads (36 mm ports) or T/E heads (32 mm ports) will most likely move your torque peak down some and help the low rev. running. The engine will still most likely be pretty weak off of an idle, but you might be able to have it start to come to life at 2000 RPM rather then 2500 RPM. I'd recommend the S heads since in a 2.4 the 32mm T/E heads are pretty tight with the intake porting unless you are running a later E cam or a T cam.
Using your cam with S heads would be similar in philosophy to some of the early 2.0 rally cars that used 906 cams with stock T/E heads with 32 mm ports. The data on this configuration is pretty sparse, but I suspect that once you were moving these cars were pretty hot. There's a fellow pelican who lives a couple of miles from me who apparently has this configuration, it would be interesting to see how it runs.
Changing to a normal S or an E/Solex cam will also help, but the large ports will still most likely make the engine a bit rough at low rev's. The porting and the cams need to work together to deliver a certain level of performance. Having one seriously un-optomised will certainly be an improvement from having them both be out of whack, it will never be as good as a properly designed configuration.
The last variable that might make a difference is your carb settings. What sort of venturi are you running in your carbs?
If you ask me it sounds like the engine shop sold you an engine that wasn't appropriate to your application.