dont be afraid to ask the exhaust shop for a flanged connection, they should be able to do either a 3-bolt, 2-bolt, or ball-type flange. my choice would be a ball-type flange, like the one flowmaster sells.

my plan is to have the two piece y-pipe welded into one piece, then have flanges put on the headers/y-pipe connections and a flange from the y-pipe to the exhaust pipe. easily removable, and hopefully leak free.