The extra "Y" is no big deal really. There isn't enough there to siginificantly increase under hood heat. Not to a noticable point anyway. Also, I don't know if you've seen show cars with non-functional sidepipes, but it considerably decreases value and oppinion. One of the lamest things I've seen was while standing next to a pretty badass 'vette with sidepipes and upon startup the only roaring of exhaust was coming from the hidden rear exit tailpipe. I chuckled and walked away.
We looked at this as if it wasn't even an option to run the downpipe to just one sidepipe.
The sidepipes are 4", so yes, they would flow plenty to just run it through one, but come on.
85 ASC McLaren Capri
79 Pace Car