Yeah was Zisco I was thinking would have been most likely to have made one. Aye you see on the likes of the safety devices cages, they arent usuallu too far from the seat. Not sure if having a bar between the two belt points would hit the seat or not, id have to see how far back the seats sat.
If it was going to be as simple as a bar between the upper front seat belt points, would something in the style of a panhard rod or C-pilar brace work so it was slighty adjustable to sit hard against the car? If that makes sense? Cause would a solid bar that fitted between those two point not be a pig to try fit in?