Hello Thomas,
I can't comment on whether seat belts were standard equipment in the Touring at the time - my guess would be no. But I think it's more important to have them, even if it's at the expense of originality.
I have fitted seat belts to my Touring 2500 3C, using an after-market kit available here in Australia under the Klippan brand, but as I used to work for their parent Autoliv, I got mine from the source. They are a fixed lap/sash, with flexible cable buckle stalks. The Klippan part number was K1517L (L is for long, but I don't think I needed the extra length). Buckle stalks are available in lengths from 220 to 450mm, but I think I ordered 250 or 300mm long. They have a website -
www.autolivaftermarket.com.
My car had already had belts fitted, so I just used the existing holes. Mounting the lap anchroage to the floor should be OK, as most kits should come with reinforcing plates, and the buckles were anchored close to the tunnel. The sash anchorage is I think on top of the rear wheel arch.
Retractable belts should be possible, but may require a reinforced mounting. I know of at least one Flamina GT, a 2.8, with retractors fitted, I believe by a previous owner somehow involved in seat belts. Options could be a horizontal mounting on a reinforced mounting on the rear wheel arch for example (there is not enough structure on the parcel shelf), or vertically behind the door, but this would require a D-ring added to the pillar between the door window and rear glass to work well, and this would also require some structural work. Certainly a fixed belt system would be easier to install.
Good luck. If you need more help, I might be able to take some pictures of my arrangement. I might even be able to purchase a kit and send it to you, as I still maintain contact with some of my former work colleagues.
Best regards, Mike Southgate