Rear seatbelt in classic 60s Mustang

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Hi, just checking with any UK owners. Did the 60's mustang come specc'd with rear seatbelt (lap belts) from factory?

Assuming not looking at pics but is there a way to retrofit? I'm considering one but use the rear seats for my kids so was hoping for 3 point seats belts but don't even know its possible with the sloping roof in a fastback...

any help appreciated. Thanks.

Harry