yeah does clip in. You would need to take it off to remove the plastic door sill. This is when i broke mine Quite fragile bit of plastic. Think the rubber seal then goes over the top.
Many thanks in advance if you have any joy
In terms of de restricting the 112mph you need a HKS (type III i think) de-limiter.
Joe had one for sale. Try a pm and see if its still available.
http://www.350z-uk.com/forum/viewtopic.php?t=1804