Make sure you've got a well charged battery and if you can, remove some of the spark plugs to reduce engine compression which makes it easier for the engine to turn over and pull the fuel through.
I would say that you wouldnt have any issues towing your friends car as far as engine and diff are concerned and if you took your time and managed to tow it without any major jerks or jolts then you should be fine.
It should screw out easily. If you try and screw the top screw whilst still fastened to the botton you are screwing against the pressure of the strut.
When refitting again screw in the top to the boot lid before offering the bottom bracket. Ps make sure you get the bracket the right way round.