I never owned a twin. I do have a single with Y pipe so I did want to add my observations:
Y pipes suck. A lot of thrust is lost. They are difficult to align and some are worse than others. They also tend to cost a fortune (something to consider in the cost factor IMO).
I may build a twin Su-27 some day but I got to say, In the few jet rallies that I have been to, it seems at least half of the twins never fly due to some issue like one tubine wont start or the RPM doesnt sync. They seem to be higher maintenance and people spend more time fixing them than flying them. But not in all cases.

I suppose a single converted twin could use a straight pipe or be on the bottom of the jet but you want to talk about ugly....

Now the side pipe, that is interesting. Seems to be the best of both worlds if it works.