If it is just highway riding and no drag strip or anything like that then there is no reason to go that big. Your build would be a drag race engine. 836cc w/ 10:1 or maybe the 915 at the very most with mild port job and a higher lift short duration cam, stock or bored stock carbs. I guess a more definitive use of the bike would help determine what you would want. Really big bores make cost go way up, and produce more heat not really something you want or need for just a highway runner. With 970 you will need aftermarket rods, heavy duty chains, cylinders need welding and then boring for big sleeves or it will seep oil. 836 is just a stock sleeve bore job and is 100% dead reliable. Why the 73 head?
Now you can send Kenny as much money as you want and I am sure he will build you what you want but why that big? More info needed on your desired purpose of the engine you are building.