With just a quick look tonight, and not being an expert, I did notice the lack of intersection fairings on the top and bottom of the landing gear leg fairings. Also, it doesn't look as though those wheel pants are the "pressure recovery types. Those things, especially combined, will cost you speed.
The non-standard engine air inlet itself might not be an issue. But if the air box inside is more early Cessna-ish than current RV, that'll steal some possible power. The manifold pressure drop on the current RV set-up is supposed to be relatively low, so that you can make good power.
The exhaust extensions certainly do stick down a lot but they end up pointing aft nicely, so someone else will have to comment. The ones I bought for mine, which are still in the box, are much shorter but have down-turned tips. They come from http://vettermanexhaust.com/
. They are four single pipes.
That ugly cowling bump needs some fairing work, too.
No way I'd stick super glue into that canopy fairing. I'd sand away as much as necessary to make a tapered edge at the damage, and then make a tapered patch over those spots using a decent epoxy and fabric. Look up DanH's postings for information on how to do that. It's not hard but you do need to follow the directions. Also, what's that post-like thing in the middle?
If you look carefully at it, the canopy fairing appears not to be symmetrical. That might not matter all that much, but it also appears as if it might be a bit abrupt. On the aft end of the canopy, a gentle slope is better than an abrupt one.
I hope these thoughts are helpful. I'd sure like to see more photos of your RV-3.
RV-3B, now building the fuselage