Hot Rod Dad, just FYI, over-scavenging means the exhaust is pulled from the combustion chamber so effectively that it also sucks part of the intake charge out during valve overlap.
As far as glass packs vs. mufflers, I have to say mufflers all the way. I ran glass packs for two years, and by the end I was almost deaf and didn't even realize it. That sh*tty-blown out sound really sneaks up on you. I had a muffler shop do a dual flowmaster exhaust for me awhile back, and they only charged $90 per muffler (so 90 for a single exhaust, or 180 for dual). That price included labor and all parts for a custom job, so I would think you could do better than $265 and supplying your own parts.
