I can't see how the tail will help reduce the pressure over no 4 TBH also the actual looks arn't exactly great, does your plenum do anything to combat the fact that no 3 always runs lean, is a box type design the best for flow or would a rounded plenum flow better leaving less possibility of hi/lo pressure areas withing the plenum? At the end of the day i wan't a plenum that is the best for MY engine, danny has proven already that he's capable of designing/building a plenum that works and is noe already updating it, also mike r sells swedish plenums for £300 so where the £1k figure came from i don't know.

The lambda probe will NEVER see the effects of one cylinder running rich as it reads the exhaust gasses which are a combination of all 4 cylinders in the case of the YB and cylinder 3 is prone to running lean but a lambda sensor will never warn you of this.

Not having a dig just trying to throw some ideas your way

Keep me updated on the development though

PJay