It's 3500ft going south, 4500ft going north.
It's a pretty tightly sliced Bravo at low level above LAX. 1500ft is the heli crossing route, 2000ft is the missed approach altitude, 2500ft is the VFR Mini Route where you talk to the tower, 3000ft is IFR, 3500ft is the Special Flight Rules, 4000 is IFR again, 4500 is the SFR's again etc.
I think Heathrow has a SVFR transit that I've heard some get, but I haven't seen anything published and I think it's an exception rather than a rule. I could be wrong. There's obviously the heli lanes that are VFR, but that's about it.