[DaleM]

You might try Andover Auto. They have kits for retractable belts and shoulder harnesses. Once you get past the annoying .WAV files with each page, look here for retrofit kits.

When I changed the interior on my 67 the stock belts would no longer work and I used theirs - no shoulder harness though.

 

[70ElkySS]

I just installed a set of Andover's retractable lap/shoulder belts in my '70 Elky. The installation was quite straightforward and easy. I haven't driven it since I installed them, but they seem to work great. I thought the prices were really reasonable, too ($65 each side + $17 for the center lap belt). I would recommend them.