Hi Tim.
One of my S1's has a spare with a strap over it. It has an internal tank, but it looks like this has been fitted around the original position of the spare wheel. I can take a few pics and measurements - but are there any specific details or reference points that you're after?
Thanks Jus
Solved the mystery today. For those with original S1 1.6HF this is the config. The straps and mountings where ther but the wheel being on the horizontal the straps did not do up. Some detective work with the parts book and the Lancia Fulvia bible showed the wheel should be angled against the inner wheel arch covering the jack. as per photo. Then the straps work perfectly! It does not look angled but it is and there is a vertical bar on the rear panel to stop the spare wheel making an impression.