I got mine from mercury as well and fit it myself (walbro 255l/hr). Not too hard to do, a couple of zip ties and a bit of thinking, 2 hours max. It comes as a whole kit (hoses, sock, wires, hose clamps). PM me and i can send u photos of the install...
Trent from mercury is running one in his (255l/hr) s15 with a GT30 turbo, and it pushes out 240kw at the wheels. I think the 040 is a bit better, but I have seen the walbro perform. They are made in the USA. get a litlle noisy (for a little unit) after a month or two...