I'm going to put a Magnaflow X pipe in place of the stock H-pipe. It is my understanding that the factory pipes are 2.5" in diameter correct?

I've attached two links to what appear to be identical items. Both Magnaflow X pipes, however one has flanges to bolt up to the axle back.
https://www.summitracing.com/parts/mpe-15437/overview/ - $400

https://www.summitracing.com/parts/mpe-10791/overview/ - $100

Any reason I can't just buy the universal $100 (which appears to be the same X pipe) and just have an exhaust shop cut out the factory H pipe and put the X pipe in place?

 

Assuming it's just a matter of cutting one out and welding the new one in and doesn't require any custom bending, then could go the cheap route. Recommend using the st-st band clamps instead of the old style U-bolt style.