it would be possible to weld on a flange BUT the exhaust isnt designed to fit like that and could crack elsewhere, the slip and spring joint it has allows some flex,
Personally i would use the J's FX pro 4-2 section or the spoon, but the OEM will also fit and work just fine on stock engines, its the cat removal that makes the difference. be prepared to get a CEL when its gone though
Several years ago there were a few failed Spoon exhausts , i saw 3 myself and all had failed because they had not been fitted with the oem spring bolts, instead normal nuts and bolts had been used, thus removed the flex from the system and caused the manifolds to crack.
in the last 5 or so years i havent heard of any cracking although people still say "spoon manifolds crack"