The car needs to be 100mm off the ground at its lowest point. So like if the sides and front bar are like 150mm but your exhaust sits at 90mm off the ground its a defect.
Take it to court but you wanna make sure everything is 100% legal because you'll get owned otherwise. As far as I know the seatbelt thing is a real thing they can get you for...never heard of the speakers though :S
I have heard many stupid defect reasons, like 'hand brake clicks too many times' and 'stereo wiring not secure' when the police man pulled it all out of its holdings (i witnessed that and my mate got off it)
However i'm pretty certain they need to show you the measurement if you request it, just like your speed if they radar you over the limit. They are meant to show you if you ask.
Anyways good luck with it all, let me know how it goes.