My wife and I bought a 1965 Thunderbird Landau sometime back with the intent of restoring it. We drove it around for three months, making notes about mechanical weaknesses that needed to be fixed and got started. First week went fine. Next, my lower back muscles went rock hard, inflexible and I hit the ground. Took steroid shots directly into the muscles (three treatments) to get them to relax enough for me to hobble around. After 'only' three months I could sleep the night through without one or both cramping somewhat...hurt enough to get me up the rest of the night. Two years back, I bought a new set of brake lines (old ones were weeping fluid through the tubes themselves) and pulled the old ones off. When I was installing a new rear brake splitter, the one just over the differential...guess what? Happened again. Sooooo, no more cars, I simply can't contort like I used to without taking myself out of action too long. That's something I simply don't have time for at my age....too much to do and see.
Bikes are another thing...no abnormal back positions required for me.
Putting the T'Bird up for sale soon to remove temptation.