Hey ag,
I completed the Shelby (Klaus Arning) drop six months ago.
I’m not sure there is any noticeable benefit, it’s really hard to tell. If you drive your car hard or race your car, yes it may.
Others may disagree, If you can’t complete the job yourself I wouldn’t pay a lot of hard earned to have it done.
One benefit the Shelby drop does if that suits you is it does lower the front of the car around 5/8” without buying new springs or cutting the springs. My car was at the correct road height so I needed to a machine and add 7/16” spring spacers to correct the required road height. I also had trouble with the UCA binding at the top of its travel (a simple job to fix with a burr grinder) and I also machined and fitted negative angle ball joint wedges. (I also increased the 5/16” bolts to 3/8” because if the slightly longer bolts)
All of this may add to the cost of the job.
I have 8” rims on the front and the geometry of lowering of the UCA and a good amount of camber may have slightly helped the tyres scrapping as bad.
I certainly don’t want to take a job off Big Al but these things need to be considered.
If you do drive your car hard, have a modified engine or your car body isn’t as good as it used to be you really also need to add subframe connectors as well.
I’ve attached Dazecars which is a great read.
https://dazecars.com/dazed/suspension101.html#19Cheers Phil.