Do you need to order harness with a special short shoulder strap(going on a fury with upper mounts behind seat).

Or what makes can be adjusted to any length?

You need ones described as Caterham, Westfield, or Single Seater.

As above^^
Four point are best IMO but if you can find ones with pull-up waist-straps those are even better if side space is restricted.
Also bear in mind they really need to be 75mm wide - espec. if you are thinking competition use - ensure they are approved for competition use before buying.
Try Rally Design, Car Builder Solutions as well as Securon & others for diff types/colours.
Cheers, Pewe

The only thing with 75mm (or 3" for us old fellas) is they are quite wide and can cut into your neck quite a bit depending on how close together the harness holes are in the back of the seat...