I was offered a pair of Mac 1 3/4in. Longtubes for dirt cheap and was wondering if there were any disadvantages to running these rather then waiting to get the 1 5/8in. ones for my 95 GT with just bolt-ons. Either way I'll be running a 2.5in. midpipe.
Without a good set of heads, you might actually see a slight loss in torque from the bigger primaries. But if you're planning on better heads down the road, and the price is right, I'd say go for it...
Some would argue that any header on a stock headed 5.0 can hurt performance. While I used to believe this, I really don't see how a good header can truly hurt the overall performance. It might lack in torque, but it should make up for it in HP. Besides, down the road when you switch heads, you'll be glad you already have headers.