Hello, it is really simple. Sorry for the late response, but i got my game just 3 weeks ago and was replacing my mech too.
The problem is all of the legs will probably break at a point, because there is a lot of movement in the amp suit mechanism.
The original toy is plug and play to 100%.
1. The mech is orginally leaning foward in a crouching position, it's move to the absolutely lowest leg position to have enough space to be mounted.
2. Stern removed the little screw inside the leg to fix the leg with a bigger woodscrew into the plastic.
3. Stern fixed the smaller part of the Leg to the mech body with two screws, a spacer and one washer.
4. Most of the movement comes from the feet of the mech.
I pre drilled the holes to fix the screws a bit more easy, stern probably just smashed anything together in a dirty way.
I try to show the pics.
Screenshot_20220628-222007 (resized).pngScreenshot_20220628-222225 (resized).png