You can spend a lot of time and money trying to mix and match. If you are looking for ease and fitment try finding one like this.
https://www.ebay.com/itm/NOS-Vintage-Yamaha-Luggage-Rack-1970s-XS650-XS750-XS850-XS1100-186/132775253511?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1431.l2649...