Seeing as how the vast majority of Enfield Bullets of any type have been sold and happily operated decade after decade in lands where getting a roadside fill up from some random guy or gal with "mystery fuel du jour" dispensed from old cooking oil jugs or soda bottles may be the norm, I think we may be overthinking this.
I seem to recall my 2005 Iron Barrel's Owner's Manual mentioning a minimum octane of 86 or 87, though I do not recall if any octane measurement standard was mentioned. But let performance be your guide: If she pings or knocks, especially under load, such as when climbing hills, then maybe step up a grade (or check your timing and carburetion).
More important than octane in most lands I'd say, is to eliminate or minimize the amount of ethanol in one's fuel, which can cause all sorts of issues, especially with older vehicles. Personally, my Bullet is on a steady diet of ethanol-free 89 octane (U.S. style "(R+M)/2") with a dash of Marvel Mystery Oil (maybe an ounce or two per tankful) to keep those jets tidy and serve as a cooling top end oil.
As already mentioned in a previous thread, if you want to check for the presence of corn spew in your fuel you don't need a fancy test kit. Just raid the pantry for some cheap food coloring, put a sample bit of fuel in a small jar or other container, add a drop of food coloring and try to mix. The food coloring will not mix with gasoline, but only with water or ethanol. If the droplet just sinks to the bottom, your fuel is pure. If the color changes throughout with a shake or swirl, you've got spew in the brew.