1982 Kawasaki KZ 750 LTD Carburetor jets

Hello, I have been working on a 1982 Kawasaki KZ 750 LTD the past 2 years. Could someone tell me what size jetting my 4 Keihin carburetors would need to fit a stock airbox and a 4 to 1 Vance and Hines exhaust? Would it be possible to make my 4 to 1 Exhaust equivalent to a 4 to 2 by putting muffler backing inside? Or perhaps I could make some sort of backing plate to fit within the 4 to 1 exhaust to restrict the air flow and increase the back pressure for a more stock setup? The carbs have the stock jetting in them and I would like to keep them stock if I can. Also how important is the seal between the exhaust headers and the engine block? It looked like someone had made aluminum foil O Ring gaskets to seal the deal between the exhaust and engine, is this recommended by anyone? As I cant seem to find the gaskets anywhere.

Ignore the pod filters in the photo below, I plan on getting rid of those headaches

With the stock air box, you might be able to get th mixture right by rain the needls a bit and adjusting the low speed screws.

I think this is the exhaust gaskets you need. 1109-1906

www.partzilla.com/product/kawasaki/11009...98b582e950b2dff6b6bf