The first thing you need to do is measure the outlet of the Factory Pipe. If it is 34mm do not run it as it will melt down the rear piston.
If it is 38mm it can be used.
Find a stock head and get rid of the Westcoast Head. You will have to run race gas all the time with the pipe and the head, you want stock compression.
You better make sure the crank, pistons, seals and gaskets and everything are 100% or you will destroy the engine.
For carbs you need to find a set of stock 787 carbs, the 720 ones do not flow enough fuel or air for the 720 with a factory pipe.
Finally what are your goals with the HX?