These elastic balls aren't that difficult to program. I do this all the time. After playing World of Goo, I reprogrammed the core gameplay in at least 5 languages/engines.
Basically you just need to do this for every connection:
fn apply_connection_force(ball1: &mut Ball, ball2: &mut Ball, goal_distance: f32, force_factor: f32) {
let diff = ball2.pos - ball1.pos;
let dis = diff.magnitude();
let dir = diff / dis;
let force = dir * (dis - goal_distance) * force_factor;
ball1.vel += force;
ball2.vel -= force;
}