Transform: Fold the grey box at the back down 90 degrees to form the lower legs. Stand with the underside facing you. Do not attempt while connected to Overflow - I did and it cost me Full-Barrel's connector peg.
He becomes a blocky Micromaster robot with a maroon chest and white arms & upper legs. He has the standard Micromaster articulation of turning shoulders and bending but linked hips & knees, but the arms are short and the shoulders low and the knees are enclosed in the grey box with just a small slot for the legs to extend out the top of. There's no reason at all for the back of the box to be closed off like this so I'm wondering why they did it..... and like Blackout & Spaceshot thinking that this pair may have been designed separately from the other Micromasters.
Transform: Fold the back of the vehicle up 90 degrees to form the legs. Stand with the underside of the vehicle facing you.
Overflow becomes a chunky blocky Micromaster with a blue chest and white upper legs. He's got standard Micromaster articulation and although the legs are enclosed above the knee like Full-Barrel there's more leg movement possible than on his partner.
Full-Barrel and Overflow were sold with the Autobot Battlefield Headquarters in 1990. Full-Barrel & Overflow were not sold in Japan.