That'll work. (Edit: the original route, not the transit.)
Personally I go very slightly further out and use Waits Farm as a turning point - I've never actually seen it, to me it's a point in electronic space identified by VORs or pre-programmed into the G1000 in the club aircraft.
Earls Colne sometimes like you to fly over or round, rather than through, their ATZ. If the cloud base is at 1999' and the cloud is freezing, or you don't have an instrument qualification, you may prefer to go round rather than over, so should plan for that.
Calling Cambridge and saying that you're at Haverhill works fine.