You have no idea how much you're asking for, or how much nonsense you're going to have to wade through when you get responses! For sound information, follow the link at 650 Central and get yourself a copy of Craig Weeks' performance manual.
First, there is no "best" setup. You don't try to run a drag motor on a short track, for example. What's best is what meets your goals, which are not defined in your post.
To address specifics, single carb conversion is not the way to make power on these motors, and off-the-shelf 2-1 systems will not deliver a power increase until close to redline. For the street, the optimal exhaust system with the old twin, whether at stock displacement or punched to 750, is 1-1/2" dual exhausts of 32" to 36" length (at the center line, as measured from the valve face) with good free-flowing mufflers. Straight pipes will deliver an increase only in a narrow rpm range; on the street they're effective for getting attention (of the wrong kind, IMO), but not for making power. The venerable Shell #1 grind cam is a good choice, and Megacycle has a new grind out that's been getting some fine reviews. Avoid that XS Performance cam from Mike's like the plague; been there, done that, and will be reinstalling the trusty Shell #1 as soon as time and energy permit. Re. porting, Jack and Craig have some fine work posted, and a little looking will turn it up.
PM if you have specific questions, Mitch; it's gonna get piled pretty deep on this thread, so I'm getting out of the way!