I have stripped down the bars I want to lower car I presume this will make wheels an axles sit straight I have swinging axle has one cv boot on drive shaft the wheels an tyres are 255/70/15. I marked up the spline and the arm 9 o'clock then pushed the arm out to relieve the tension its sat at about 20 to 9 now when take off spline does it need to be moved up or down how many teeth or is it a case of try an see thanks

You have 40 splines on the inside end and 44 on the outer so adjustment angles can be as low as 80 mins by turning one one way and one the other or you can get 8 degrees 10 mins or 8 degreees 90 mins depending on which end you turn.

On swing axle the wheels are best vertical or slightly negative camber.

Peters manxmaniac site has info on it and a search on here will bring up loads of info.

The hardest part is getting both side equal as the right bar may be softer after driving one up most of the time.

Do need specialist equipment?
How do you prevent the bar from untwisting and therefore, loosing the original position?

The bar is solid nothing to twist or bend. What I do is once the spring plate is off the casting and hanging at rest is scribe a line along the top of the plate onto the casting behind it. That way you always have the original position marked should you get lost. During the job.

No specialst equipment unless you are lucky enough to own the vw adjuster tool that allows  adjustment of the tracking by a threaded bar rather than a knocking stick to line it up