To hard to determine exactly like ride height sproket condition etc. I got a kfx 450 RK chain on ebay 22 bucks, they run 120 links which is plenty. just look for a 520 pitch 120 length chain and cut to size. I would say somewhere like 96-98 maybe.
2 links adds about an inch. You cant add just one, well you can use half links but in rare cases. 92 is actually stock length. with 14/40 its kinda a pain on my chain it was either tight or too loose. So you will need +4 links but might be too tight or +6 thats where I got 96 or 98.