We have a 67 Cadillac that obviously only has lap belts, and we will have two kids in seats. We could just avoid the whole issue and not have them in the car but there are a few in town cruises we would LOVE to take them on. One kid is in a booster and one in an infant seat. I think we could install the rear facing seat just fine but not the booster. Has anyone added a shoulder seat belt? Went without? What are my workarounds here?