Do 6n rear coil over fit a mk2 polo

I think you need to change the bottom bush and they will.

even when at the top of the threads the car will -80mm , just a warning.

its for bags actually man just got offered a set or rears and compressor for 200 was hoping they would fit

Will physically fit yes, although you may want to space them down as they're shorter, you could find you often top them out whilst driving, especially on air as you won't be fully slammed whilst driving around.

Also the lower bush is narrower than the gap in your mk2's rear beam, so would need a spacer (only one side to prevent it from being on an angle)