The floor is rusted at the original jacking points. Where can I alternatively Jack the front of the car and place jack stands?

It depends a bit on what job you're doing on the car. You can use bottom arm mounts or anti roll bar mounts, but they will cause some chassis flex. A pair of ramps may be a better option. 

The wheels need to be lifted as well. I want to briefly lift the car to replace the brake pads.
If I jack the car on the place pointed at by the red arrow and then put the jack stand under the place of the green arrow I'm doing what you suggest ,right?

 

Useful question! My sills have just been painted and I don't really want to jack it from there either. Have put trolley jack under the gearbox before but not great for drivers side wheel and probably not a great idea for more than a few mins!

If you're just doing brake pads, I'd jack it on the ARB mounts and stand on the outer ball joint of the bottom arm. 

Cheers, when eventually get mine back it's going to need new tyres and don't want to damage fresh paint on sills.