Understood. I was thinking of anchoring the eye bolt in the floor and running the straps up through footmans loops just below the trim strip, backed by a full-width extrusion on the other side of the firewall.
My thinking being drilling 4 small holes the through the firewall would be less traumatic than cutting 4x3" slots. Mostly because that would expose the nylon straps to the oily/heat goodness that is my engine compartment.
Both my seats are right up against the firewall. The eye-bolt and clip is at least 3". There's plenty of room for it on the floor. Behind my seat, not so much.