You can't shorten the neck via the tuning slide any more. Have you discussed this with Blashaus?
Their necks are quite expensive, much more than Gloger:
Gloger necks are 650 ($709.00)- 850 ($928.00) Euros
Blashaus necks:
1465 CHF ($1,685.00 )-1865CHF ($2,145.00)
Blashaus should be able to accommodate you, these are "boutique" necks.
What was your your goal when you decided to replace the original neck with the Blashaus?
I've given up on all this with my old BC, and purchased a new Kessler last month
- Low C! for~$ 2,700.00 shipped.
The Kessler plays great top to Bottom with my Fobes BC mouthpiece, intonation is excellent.