Needs to be a YZ-D/E/F, IT or monoshock DT barrell to fit the cases.
The IT125 and YZ125F barrels also require a different exhaust/exhaust mods.
The DT barrells have a smaller intake/reed block which won't accept the YZ carby.
The YZ-E barrells look different from the outside, which gives them away as being not-pre-78 legal (if that matters).