the wall thickness of the coupling is going to be 3mm so 6mm total there plus the 90 mm for the throttle body and You are going to have to add an additional 5mm for the wall thickness of the throttle body which is 10mm of wall across the diameter.
so 90 + 10 + 6 = 106mm
The only places you need to use a constant pressure clamp which is what those clamps are is at the connection to the turbo. This is because of thermal expansion and the clamp getting stretched if there is no spring on it. The throttle body doesn't get hot enough to have that issue. Not to mention space is really limited where that clamp is and trying to get that one with the spring down in there would be a royal pain.
I have something whistling in my car as well. Mine sounds like a steam ship whistle. It's as loud as one is as well. only happens when i get into the high teens for boost pressure. I think I need to get a siny bit larger o-ring on the TMAP sensor. It's not as snug as I would like it to be. I am going to do that tomorrow morning on my way to emissions.
I have not let mine go past the 15psi when it started. I had thought that it might have been one of the vacuum line connections at first because I changed everything over to AN fittings and there are a lot of compression connections. 6 in total 3 for the boost control solenoid and another 3 on the bypass valve solenoid. I have them tightened up really good. I may have to check them again. I didn't make it to emissions yet as it was 18 degrees out yesterday and not ideal for working on the vehicle. I may take the car for a couple hard rips around the block to see if I can get whatever it is making the whistle isolated. If I can get the pitch to change on the sound then I know I am messing with the thing that is causing it.