Heres a pic of the intake boot.Think its off an 82 RM465.Think the 83 RM500 are the same.Fits 38-39mm carbs and likely be able to cram some bigger in too.This is for the 87 5 bolt only.

Just look for part number 13110-14210

I should add this boot doesn,t have the "wings" on the back side so if you run the stock cage might have to run a reed stuffer.One of the builders would likely know for sure.The V2 setup would be fine.Jerry sells a sweet V2 reed setup with spacer plate.