#1, the springs may very well fit, but id say they would be different strengths and therefore would be firmer or softer and sit at a different height.... ect
and #2, the lid just unbolts via the allen screws and then yes you can spray carbi cleaner into it. one suggestion tho, is that you pull the spark plugs or you will get compression lock from the fluid sitting in the head/valves. i learnt the hard way and nearly burnt out a starter motor. another suggestion would be just to undo the intake pipe (unplug the maf) and spray into the TB with the engine running and bring up the revs while spraying or it will stall.
i did it that way to my wifes VX. cleaned up the plenum real nice.
edit, just re read your post, if its real gungy and oily in your plenum perhaps its time to look at a rebuild? that mess is usually caused by a lack of compression creating blowby and thats what your PCV breathes. and that means your engine is also breathing it.