Depends on if you have an early or late 084 piston. The early 084 piston uses 1.5mm thick rings, which is what the 3120 pistons use.
The late 084 piston uses 1.2mm rings. The 3120 piston is also quite a bit taller than the 084/088/MS-880 pistons so you would
either need to cut the squish band in your 084 jug or turn the crown down on the 3120 slug.