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Re the filter position, if you are sure you have a clean tank it's reasonably safe to allow the filter in the pump to strain out any big bits that might come through. If your Pierburg has the removable top you can check the strainer now and again. Note the word strainer as it won't filter out the finer particles. That's where a filter between the pump and the carbs becomes useful. Fine rust and sandy particles are stopped from jamming the float valves and settling in the bottom of the float bowls. The SU is very tolerant up to a certain size of particle but you only need a few clumped together to give problems. The factory just relied on the pump strainer. Then, the whole system was clean, and you fed it with clean petrol, so no real need for anything else. If you know or suspect that your tank is dirty/rusty it's best to try and fix that by the best method you can afford. At least take the car out for a bumpy ride and then drain the tank to see what comes out. That will give you an idea of what sort of problems your likely to have. If bad, you should be able to improve the situation by doing the drive/dran proceedure a few times. No way a cure and putting a filter both sides of the pump should keep you moving but keep a couple of spares with you in the car. Fine silt will clog a small filter in only a few hundred miles.
Filters about 3" x 2" are much better value than the smaller ones.
"Bearing noise" 55 - 62mph is a very common speed range for resonance on the Amazon. It can show up as a sort of coarseness to something in the car buzzing in sympathy with it. Exhaust systems mounted too tight is one reason. They should be "floppy" so adding the extra mount from under the rear bumper to the end of the rear pipe completely changes the resonant frequency of the system. Papa Volvo knows best so make sure none of the mounting rings are pulled tight. It should "hang from them.
A combination of a soft gearbox mount and a tired propshaft centre bearing mount can put a varied load through the centre bearing. This can cause a drone, especially if it's starting to run a bit dry.
Unfortunately these noises can be hard to track down and often end up being somewhere completely different to where you think. I would pull the gearlever boot to see if the noise is more obvious through the hole.
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