This is a replacement torso for the Black Series IG-11 to upgrade him to IG-12.
I added holes to glue in magnets to attach the backpack. Magnets I used have a 5mm diameter and are 1mm thick.
Legs, arms, and head should fit just heat up the print and pop them in and it should have a snug fit.
I used a Black Series Grogu but you will have to trim him down to fit.