Any plates that fit a 12L3/4 will work, I just got the IRS 4 bolt plate conversion plates to replace the ones on my YRX12 WE because the ride hieght adjusters are loose in them. I wish I could keep the Yok ones because they are lowered more than any others.
You can use an IRS big ring diff to replace the stealth diff that comes with the Yok; and you can get it in blue to match all the other parts on the WE. Or for the best diff of all, get a Niftech (but no blue). You will need to replace the right and left hubs as well.