Well this is a true dual exhaust set up which will require two catalytic converters which this kit doesn't provide. Plus it's reduced to a final pipe diameter of 2 1/2, which will inhibit power if you ever choose to upgrade to a 350 or an engine of a higher displacement.
A good rule to go by if you've got a 305 and want to upgrade in the future is to choose an exhaust system that can be swapped over with either no modifications or minor ones. This is obviously done to save money in the long run.
So you'll generally want to look for 3 inches in diameter for piping. Of course this can be argued through backpressure and exhaust theory, but that's another story all together which would require something more than "cheap".
You'll probably want to look into a different muffler also, go with a hooker max flow
http://www.jegs.com/i/Hooker/520/21606/10002/-1
or aerochamber
http://www.jegs.com/i/Hooker/520/21505/10002/-1
both boast very good CFM flow numbers compared to straight-pipes and other aftermarket mufflers.
Hope this helps.
