cl450 scrambler exhaust 2-1

[dumbkid]

I just picked up a scrambler exhaust for my 1974 cb450.  It's from the scrambler of the same year.  I would like to make it into a 2-1 exhaust.  I was planning on just picking up a Y-adapter and working from there.  So I've got a few questions.

1.  I would like to know what size diameter the single exit diameter of the Y should be, if that makes any difference at all? 
2.  Muffler recommendations?
3.  Online vendor recommendations to purchase 2-1 Y-adapter. 

Here's an example of what I would like to do with the exhaust, but most likely a different style exhaust.

[TheBullitt]

Yo!  I'm looking to do the same thing to my CB350.  I got the CL pipes and want to add a collector and run a single muffler.  I found (from another post on DTT) a company who makes them; http://coneeng.com/pdf/motorcycle/MC%20Collectors%20PDF.pdf

I'm not sure exactly which ones we need.  My other question is, can I run the whole set-up without a brace somewhere else - ie only connected at the engine.  The stock headers are damn solid but I'm not sure if that would put unnecessary strain on the engine...anyone?

[Swapmeet Louie]

you'll need a slip joit on one pipe,they are both at about 30 degree so they won just slip into the head if they are permenantly connected.