3 questions regarding headers flange and exhaust
 

Hey mates, my exhaust is shot on my 350 chevy, and I got given some headers and dual flowmasters.
Any way the header is 3" O.D. but no flange and im wondering if i need to weld it?
The flowmasters are are 2.25" OD, as well the pipes for it, aswell are the stock pipes on my truck..

Also since my stock pipe is a single 2.25 would it hurt it to reduce the tips to dual 1.5' or better to leave it 2.25'?

One more questions. would it make any noise difference to use glass packs and the flowmasters?
I'm going to have to cut the pips in half because they come out near the tires and i want them straight back.