I played around a lot looking for 90g, but I've convinced myself it's impossible.

Two min length arms seems to be the minimum arm requirement, you need to be able to reach all 4 nodes of the Animismus glyph, either to drop off a single salt or to grab a single Vitae/Mors. So each arm needs to be able to handle single elements, but those arms are too short to pass single atoms back and forth. So each side needs access to a bonder, so they can build large enough components to pass across the glyph. But they also need to be able to grab a single salt to use the glyph, so they both need access to a debonder. That means we need at least two arms, two bonders and two debonders. That's 100g already.

At 100g you have quite a bit of flexibility, I think stretch arm is probably best so I ran with that, though there might be an argument for having a third arm instead.