Lifter material

[Ocracoke]

It would be all in the construction as how rigid that'd be.

HDPE probably wouldn't work as well here because of how flexible it can be (say the load on the mechanism was off centre for example, that'd warp it I feel). That being said, given the thickness you mention, it might be OK but I can't think off of the top of my head any lifters who use HDPE in the mechanism.

The box section, I think, is going to be lighter overall (since it is hollow) and more rigid, at the expensive of impact absorption as you mention.

Not a 4 bar lifter but Snappy is a good robot to take a look at for this sort of build I think.