As dale said, I did manage to remove from above with a mix of extender arms and Uni joints from my socket set. You will need an actual o2 sensor socket rather than using a spanner
Fujibitsu legalis R is by far the best system. Straight bolt up proven to flow over 300kw atw and a nice sound with absolutely no drone and is legal volume. If you get one and need it fitted bring it over and I'll bolt it up.
Don't put thermos in your car. It has been proven with our cars over and over that they can not pass as much air as the standard clutch fan setup. Everyone who has done it has than changed back to the stock fan setup
Have you tried changing the vac hose that controls the bov? Some m35s seem to have a restrictor in it. Mine was one. Removed that and shudder went away.