You are travelling far back in time. 
This setup, along with the Tentacles - #3 by marcus you found are using the old “rigid” mechanic, before Markers were born.
There’s very little new or difficult things here; the character is setup like any other character with Ragdoll today. The official beginners tutorial is still relevant here: Manikin I - Learn Ragdoll
For the feet to snap to the big capsule shape you’d use the Attach Constraint.