the long rod kit is no longer a valid part number, and the spacer is getting phased out.
If I can remember I will post the part # when I go to work tommorow. Or you can go to your local Yamaha dealer and ask them to get on the Yamaha Dealers website,go to parts,go to clearance items, go to offroad accessories and look for the '97 spacer.If the 97 and the 90 use the same base gasket you're set.After these go they will not be available from Yamaha but I believe Cometic gaskets will cut you one relatively cheap compared to making one.
Once a a particular model is updated or redisigned the GYT,ABA or YZR part numbers get swept under the carpet, if they can no longer apply to the current model and they are very difficult to locate unless you happen to have the Yamaha Accessory Catalog for that particular model.
Also if you are going to use the 89 & earlier rod in a 90 & later engine you will need to make a longer powervalve actuating rod and its cover.