About to order Koni struts and shocks (yellow) without the ground control option to replace the KYBs that are on the car now.
I'm also going to replace the sagging rear springs with Weltmeister 100 lb springs. They are ~15" long, which is shorter than stock, IIRC.

Without a threaded collar, the Konis are limited in their height adjustment. Is it going to mess up the ride height in the back (too high or too low)? Anyone else running this setup?

I would go with GroundControl adjustable Koni's, It's a great setup and priced well, with any spring rate you want. Best, MarkClick to view attachment

if you are seeking the perfect ride, given we have tweaked chassis from side to side...I would also suggest the adjustable spring perches.

This gets you into a much wider selection of spring rates, for pretty low cost per set.

You can then, finally, properly corner balance the car...
you can also set the ride height to exactly what you want.
Rich

I have a set of Konis with the standard adjustable perch via clips and 100 lb springs.

No issues getting ride height where you want it for street use.

I know there are many others on the site using the same Koni’s without issues. Surprised no one else has chimed in. If you search the site I’m sure you’ll turn up plenty of builds that used the Koni’s without the Ground Control threaded perches.

I wanted it a little lower with my 200# springs. I had a machinist cut two more groves into the shock body the same distance apart as Koni did. I am using the lowest grove I had cut.

im not sure what you are intending to use the car for...but threaded perches really do help adjust for the 200lb driver when properly corner balancing a car.

If you have never driven a properly corner balanced car, properly aligned, you are certainly in for a treat when you finish.

rich