My 2 bobs worth on that plenum assy.
It looks all wrong. It's angle relative to the direction the airflow has to travell is too severe to me. It may have the actual correct plenum area, but just not put in a practical position. No.1 cylinder would get a different air signal than No.6 cylinder, wich means you'll have to run an ECU that trims injectors for deficient balance of the engines breathing hardware, which is a bandaid approach for a balanced setup.
And the 80 or so mm throttle body mount is in my opinion way too large for an RB20/25.
That's my thoughts on these type of plenum assemblies. And the fact that they are so much money to buy. Waste of time.
I have a modified stock plenum assembly on my race car, check that out on my RB Racing post soon.
Turbine.