Not the first and certainly not the last to do so!!!
Got a Motordyne Plenum Spacer for ZMANALEX (usually great service) it's the 5/16" ISO Thermal one. Installed it today and am pleased to say it went (almost) without a hitch - I managed to round off one the engine cover bolts as I had to rush toward the end! Ah well, not the end of the world, will sort it next week.
Not done the coolant control valve yet as ran out of time.
The car felt great afterwards; I'm sure it had a slightly deeper growl and seemed to pull a bit better. Didn't get any CELs or anything so all good.
Really pleased with the mod, and got a bit more confidence from doing it - never had the lower plenum off before, but all went well.
If I can offer any advice to anyone thinking of doing it I would say this: I don't have much mechanical experience but was able to do it in 2hrs without any problems (apart from being a bit clumsy with the aforementioned bolt!). The instructions included are very clear and easy to follow.
Apart from normal hand tools, I would recommend investing in a low range torque wrench with a range capable of 4-5 NMs upwards - this is to ensure the bolts are tightened properly so the seal is good.
Oh and leave enough time to avoid rushing anything...schoolboy error there!
Happy