Here are my thoughts if you wanna stay stock use wiseco if you wanna go big bore I would go with je.
Standard bore wiseco-https://www.ebay.com/itm/Wiseco-Yamaha-83mm-Standard-Bore-for-Warrior-350-1987-2004-10-25-1-Comp-/233210890362
85mm...
I used to refer to this forum all the time just never made an account because I figured it was obsolete. But now that things are kicking back in gear because people on Facebook are irritating. I've decided to make an account.
You're better off updating your harness and flywheel and statorto a 97 and up. Just because it's way easier to find electrical components if needed. You can buy a new harness for 150$ I believe. That's what I would do if I was in your position atleast.
What rear shock is in this beast of an 87? I would love to own an 87. I just don't have the time to build another one at the moment. Very clean bike my man!
The older bikes ran a 2 cable design where the newer ones run single cable I would definitely consider buying a new updated cable that doesn't split into 2 so you don't have to worry about the Hassel.