I wonder if it would be possible to build an airbag system into the horn button area on a TR... I've no idea how much space those things require - I imagine you have a small charge attached to a folded up bag, with some wired link to a G-force impact sensor elsewhere on the car. If the bag and charge unit could be made small enough, it might be worth looking into. I wonder what the smallest commercial unit size is....
Just did some quick internet research and have come to the definite conclusion that this is a REALLY BAD IDEA. Airbag systems are designed by experts for a specific model car - they are not generic. The experts design the airbag location, airbag sizing, and location of the deployment computer to which they are connected - all things that us garage guys shouldn't tackle.
Also learned that there is apparently a LOT of airbag scams out there on vehicles that have been in an accident where airbags have deployed and the car or truck has then been subsequently repaired and sold. The cost of replacing a deployed airbag can apparently run to $1,000 per unit, and at that price, its just too tempting for a shady operation to stuff the old deployed bag back into its cavity (or fill it with paper) and disable the airbag warning light.