I don't know that I would mess around with a kit from Rock Auto. There is awesome aftermarket support out there for these motors. I don't know what that $750 kit includes or what exactly you are looking to replace but regardless you can build it way better for practically the same cost of OE replacement parts.
You also have the choice to totally scrap your cylinder heads and simply buy new heads. You also have the choice to totally replace your shortblock/longblock. There is a GIGANTIC new and used market out there for all of these options.
Check out vendors around the website.
A huge company that sells tons of internal kits/shortblocks/longblocks for our car is Modular Mustang Racing
I would also check out Diamond Racing
Clevite for bearings. ARP for studs/bolts/hardware.
The list goes on.....theres TONS.