I've a Librands system on my 4/4 Sport. I know it's not the same as the Plus4 but the noise issues at speed are much the same and I am currently experimenting with silencer dimensions to see if there is a nice half way house between the standard system and
Librands.

I'll be interested to see how you get on with the throttle bodies both in performance gains but also noise wise as well. I'm in discussion with Mark at the factory at the moment about a setup for my car. Just need to have a chat with my insurers first!

Jays
Former Morgan owner. Gone but hopefully not forgotten!