Dart heads in general are very good quality thick high perf castings. But they do need a good going over to get them up to snuff from out of the box , as cast form. The SHP head is not the same as the Platinum,, Pro 1 stuff.
I would look at some other stuff before you buy. The nice thing is you have lots of choices and all winter to research.
Any thought of using a spool on the street is a deal killer. Same with the flowmaster crap mufflers .
These will kill the real power more than any thing. There are way better mufflers. Especially if you like to and plan on "Driving" your car.