I have a 4 into 1 Mac on my 77 550K. I don't know about clearance issues, because I bought the bike with the exhaust. I don't particularly care for the system however. I don't know how old mine is, but it's pretty rusty, loud as sin (no baffle, removed by the PO) and IMO beyond ugly. Maybe the chrome ones are better, and maybe they are better than what I think, because I have no experience with them beyond what is on my 550, and it came to me in the shape it's in.
Here's a pic:
Now alot of the discoloration on the pipes and muffler is dirt, but there's a lot of rust on there too.
Jeff