Sorry for delay in replying, can't find any obvious attachment points on the front seats - but then I'm not sure exactly where the location points are, anyone got a pic ?
Car has the original seats and build sheet shows belts as a fitted option.
You should have two plastic retainers above each door for folding the static part of the shoulder belt behind and a little plasticky rubberish pouch type thing for stowing the clip in. The anchor point is sort of above the door shut. the are in a line so you should have anchor point, clip, clip, pouch above the window.
At low level, you will have the anchor point just behind the rear of the seats for the static part of the lap belts. You will then have two straps bolted to the floor on each side of the console just behind the seats. These two are the parts with the release mechanism.
I am not going to my car till the weekend mate, but if you can hang on till then (assuming no one gets there first) I will photograph everything you need and mail it to you. As far as interchanges go, my manual doesnt refer, but I would imagine the belts from any 70 B body with buckets will do. These are parts which are very likely to be in the "parts bin" category. Just remember, there are twon separate belts for each seat, a lap and a shoulder. So there are 8 parts (4 buckle bits and 4 clip bits) and you are looking for 6 anchor points (4 at low level and 2 at high level.)
You should have two plastic retainers above each door for folding the static part of the shoulder belt behind and a little plasticky rubberish pouch type thing for stowing the clip in. The anchor point is sort of above the door shut. the are in a line so you should have anchor point, clip, clip, pouch above the window.
I just bought a complete set of original gold seat belts for my 68 Charger, they were filthy so aved them in the washing mashine - they have come up beautifuly, even removing tar stains etc!
fitted some recoiling belts in my Charger as the orignals are a pain and not as safe. They are special ones for pillarless car so they work a treat
I may have the old belts somewhre but they were green ones and one or two pieces of webbing were damaged . you could always get the webbing replaced by that place in Surrey that mends seatbelts.
i may even have another pair of those recoil belts . if anyone else wants to upgrade.