Jetting for stock air box and Vance & Hines header

What jetting is best for a 1976 kz900. Stock air box and Vance & Hines header? Thanks

Air intake effects jetting far more than exhaust. Four strokes just want to get rid of exhaust gases ASAP. As long as you plan a free flow tail on the headers you'll be fine with stock jetting. 

Yes as You've already stated. You've kept the original "Golden" airbox! As Warren stated, You want that combination, intake constriction is far more important then choice of Exhaust. While Vance didn't flow quite as good as an ole Kerker, keep the original jetting of pilot 17.5. Going to a 20 on stock engine will result in sluggish overfueled scenario. I'm assuming You have the original Z1200 1976-77 carbs? Should have, as original, 5DL31-3 Jet Needle and 0-6 Needle Jet. Standard main is 115 and pilot 17.5. Didn't mention a packed baffle, loose or pulling it out altogether? Assemble and check for full WOT. 

Packed Vance now. I plan to remove the packing and open it up. I restore 2 strokes. I’m going 4 stroke now. Any advice would be appreciated. Thank you

Thanks

Agree many 4 into 1 systems do not require jetting changes but you will not know until you try