To the contrary,
itís quite easy to make and exhaust for the Kawasaki FC420v & FC540v.
Buy a used muffler assy on ebay. Make sure it has the elbow. The elbow will discharge to the left or right. Make your flange connection from the mating flange from the muffler.
I have made 10 or 12 of these, Itís easy and relatively cheap. Works like a dream. Awesome flow with little to no restriction.
The Elbow for the 540 is no longer available. Not sure about the 420. They show it still avail on some parts sites.
I stocked up by buying used mufflers anywhere I can find them, used on Ebay, craigslist, I got the last few in scrap yard.
The last one I got was ebay for $12.95 and a few bucks shipping.
The Elbow is the key part -Kawasaki # 49062-2057-9Y , approx $43.00 and well worth it.(Jacks Small Engines on line)
I would get a couple spare exhaust gaskets too.
You can look up parts at Kawpower.com