Is there a fool proof method of determining where to cut the hole in the body for a right hand tank?

Is the method of making a template from the left flipping it over and marking on the right reliable?

What's the standard hole size? 70mm, 2 3/4"

I'd be making a template from the left side and transferring to the right.
The tank will have a small amount of movement inside to correct for the hole.

Only reason I'd do it that way is because if the holes arent symmetrical one side to the other it would give me the irrites.

I did mine with a paper template.

Remove your LH tank and make a template that uses known comments points. Like the windscreen or the fold in the body below it (for lack of a better name), the seam and the boot. Flip it over and use it on the other side of the car. Make the hole the same size.

The tank has a little give as said above so fitmet can be a bit off but be careful. I got it right the first time so can't be too hard!

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1964 Morris 850, 1330 Supercharged - 81.8hp atws.
1975 Leyland Mini S 1100S powered - Nice and reliable.
1977 Leyland Mini LS - Project LS-T

Use masking tape to make the template as said above, layering strips to match the body profile. You can't make a decent curved 3D template from paper or cardboard.

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Too many cars, and too little time.

Wouldn't work AWD, the curved tape template wouldn't fit to the other side.

It would if you used double sided tape. Just reverse it

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Simplify and add lightness

Did mine last weekend, paper template, 2 5/8 hole saw.
all done in about 1/2 hour.
Thanks to morris for going out in his cold shed for some measurments