I'm currently doing a spindle swap on my 88' using 400ex spindles/hubs and yfz450 brake calipers.  The OEM upper ball joints should work.  Last week I got the lower ball joints in the mail.  I had to get 400ex lowers that are for after market a-arms.  I haven't tried mounting them yet, but I'm pretty sure they will work.  They obviously fit in the 400ex spindles and the a-arm mounting looks to be same as OEM.  The dual piston yfz450 calipers will work on the 400ex spindles without any modification.

This is as far as I've gotten.