I wish to swap my 5.5 gal fuel tank in my 1977 Clubbie for a 7.5 gal one. I'm pretty sure it is a straight bolt-in swap, but does anyone have a picture of its installation? I'm curious as to how the spare wheel fits in the boot next to the bigger tank.Also I see in the Parts catalogue that there is a diagonal mounting strap. Can I use my existing mounting strap?

Well, the 1275 LS were factory fitted with the larger tank and also had 12 inch wheels including a spare in there!. You will not have any problems fitting Spare in the boot with big tank.

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The bigger tank fitted to the 1275LS was just held in with the same strap as the smaller tank.
Later on the UK started using the diagonal brace to hold them in.
There is no reason why you can't use the original strap.

The spare wheel in the 1275LS was a tight fit when using a big battery but it fits snugly.

Thanks for the info.