I helped my friend install his HotShot Header last week. It sounds great with his HKS Hiper and downpipe.
To clarify a few things:
1) Hotshot upgraded the header design (maybe 3rd generation) but did not upgrade their instructions. It suggests getting new gaskets but they now include all that is needed.
2) It meets at the bottom and connects to the Cat, it won't replace it. If you want, get a downpipe.... sounds so much better w/out the cat, imho.
We messed around with the install, took us 4 hrs because the hardest part was removing the AIV, EGT, and getting the 10+ yr old bolts loose from the exhaust manifold (PB Blaster works wonders!) Once everything was off, only took 45 min to install the header. We also went parts searching... long story, don't ask. Haha
Don't forget to wipe it down after you install, don't want the fingerprints/grease to burn into the header when it gets hot.
Congrats on the purchase!
-Aaron
'91 240sx coupe