I think that is a very nice kit. There are many members who have done similar upgrades. If you do a search regarding any aspect of upgrading the 300, you'll find ample information you may need.
I would install studs for the header, with crimp nuts. You'll also need the oem large washers. You need to grind down one side so it will sit flat; header flange and intake flange are different thicknesses.
Consider your starter. Buy a new one b/f the install b/c of the header heat may affect it.
I think I'd get the 4v spacer that separates each carburetor bore, rather than the open type, otherwise you're defeating the purpose of the dual plane manifold.
You'll need a heating plate to mount on the bottom of the intake and run coolant through it.
You will most likely need the throttle cable bracket sold by Lokar on Summit Racing dot com.
Note: Nothing will help that kit like a good port and polish of the head, and a mild cam. However, I'm sure you'll see a nice improvement over stock just as it will be with the kit alone.
Good luck. K.