Mike – Apparently that 165/80R13 size is pretty well obsolete today in terms of "regular" tires, that size would be ideal.
The spare in a Tiger lays flat, unlike the Alpines – thus the issue with the false floor.

quote canbeam:

I just went with a cheap and cheerful solution, and bought a no-name 155/80 13 tire from Walmart a few months ago. Looks good, fits under the false floor, holds air a lot better than my 1970’s 165 Michelin ZX…lol, and the diameter is close to correct.

Thanks for the input! Your spare was actually even a little older than mine 😯
That provides 1 possible solution, ^^ is also the "alternate size" offered by the Tire Rack. The guy was a little hesitant about the lower(?) load rating, he said it is for some VW… but it is the spare [which I hope will never touch the ground], and I would be for sure taking it easy if I ever had to use it.

Is anyone using a 175/70R13 spare in a Tiger?