The Katyusha is originally a MechForce UK design, which means it's a lash-up of different bits made back in the 1980s.
The original Katyusha model was made from:
- Unseen Marauder torso & most of legs
- Kodiak-based arms & feet
- Missile pods from the Unseen Longbow
with a degree of interpolation (eg. the cans on the knees). I may post a pic in another thread, not to detract from Ava Mango & Savage Coyote's work.
Ava Mango appears to have used:
- BattleDroids Marauder torso, legs & feet (enhanced by 'knee cans'
- Kodiak arms
- missile pods from some other mini line.
The Katyusha was armed with an MRM in each torso, three MPLs in each arm, an MPL in each leg, and a MPL in the CT.