Late model swap -- belts mounted to seat

[kst8engineer]

Help me out, guys -- I'm looking for ideas. In my '71 Chevelle, I'm looking to upgrade the front seats and the seat belts (it only has laps in the front currently). I'd like to improve driver restraint (and comfort) in the seat, so I thought about using some Corbeau-style 4-point belts, but I can't since the back seat has to remain usable for my kid(s). That means no roll bar, and no "straight back" tie-in for the upper seat belt straps.

I'm wondering about swapping front buckets out of a newer vehicle that have the shoulder strap retractor built into the backrest of the seats. I've seen a few vehicles like this, but I'm not sure what (my Mom's Buick?!). Help me think of a vehicle that would have well supported (well bolstered) seats that have the shoulder strap retractor built into the backrest of the seat... Any ideas???

Thanks in advance!
Galen