I have an 18mo old daughter who is in forward facing carseats now. I would really like to take my '68 fastback out more but I can't take her with me. Does anyone know what carseats work with the bulky stock seatbelts and confined space of a fastback back seat?

 

If she is big enough for a booster seat, your stock belt could work. You may look into some 3 point belts all around. I put the non retractable belts in the rear of my coupe for the kids. They get adjusted to fit every 6 months or so and both kids know which side is their side for fittment purposes.