Yes, the rocker panel on my '68 is in good shape and that is the jacking method used in the original manual.

I have been driving trucks and jeeps( iron everything) the last 20 years and am enjoying the Mini as a new hobby.

I guess they are not as delicate as they seem.  

Are you looking at the slot in the sill (called rocker panel in USA) under the passenger door? If so,  the original jack fits in there nice and safely if done right.  Open the door first. That gives you room to turn the handle round and round.

Use this original method if you know for sure that your sills and frame are not rust-compromised.

See scanned image from Haynes Manual

Thank you. I want to check my brake linings.

Those I see are long narrow coil springs, almost like a heavy-duty screen door spring.

I tried jacking it and the wheels articulated widely as the springs expanded. I am used to Chevy trucks with rear axles and am new to classic Minis so I did not proceed without more research.

The original owners manual method with the original jack looks a bit menacing and I don't see how they avoided accidental jack slippage back then.  

I don't know what you mean by "little coil springs" unless you have hydrolastic suspension.

Starting on a level, solid surface, with a single jack:
1. Chock the front wheels.
2. Jack up one side of the car with the jack under the wide side member of the rear subframe.
3. Put a jack stand (or large solid, stable block of wood) under the same subframe side member, clear of what you need to work on.
4. Jack up and support the other side of the car per steps 3 and 4.
5. Before getting under the car, push on it firmly to make sure it is stable and won't rock.

Do not attempt to lift the car with the jack under the subframe cross-member below the bumper - it will buckle.

I have a '68 Mini and was wondering what is the safest way of jacking up whole rear end of the car with a single small floor jack?
Are the little coil springs stressed too much by doing this?