Ok I just got off the phone with David at Mac's Products. You do not need the adapter plate. That is only for the adapter muffler. He said that web page is old & that they need to change it because it tends to confuse alot of people & that he gets asked this question all the time. I wanted to speak to them about a pipe question I have anyway so I asked him about yours too. That muffler #6590 that I just mentioned will bolt right on to your Evo .46 engine. Now keep in mind that this is not a tuned pipe it's just a muffler, a very good one, but it is a muffler not a tuned pipe. If you wanted to go that route it will cost a little more $$$

The header will cost you about $29 & the tuned pipe will cost about $46 for a total of $75. You can get the quiet tuned pipe for about $30 more or the muffled tuned pipe is about $20 more. But the regular (louder) tuned pipe & header is about $75. This tuned pipe set up will enhance your performance a good deal though. They have a link telling you exactly how to tune the pipe to your engine as well. They have already done all the research & testing for us so that you can look at their tuning page & just cut your header to the length that gets the most rpm for your engine. I just looked at that page & I see that they don't have the Evo .46 listed on the tuning page yet. So if you wanted to go with the tuned pipe you might want to give them a call & speak to David for correct info on tuning for that engine. He was very nice & helpfull on the phone, I'm sure he will clear up any questi0ons that you might have. His phone number is : area code (916) 456-6932