nice bike and very good job on the full restoration
It's from 1996, as there isn't a lot of documenation about Kästle I'm happy to share a few bits
The test result (picture from Google translator) isn't great, but this is only a matter of the a bit cheaper components in particular the suspension Fork to provide an attractive price
The higher equiped Kästle FS had all Marzocchi MX or DH forks. I would give it a try with a better fork, maybe even up to an early Bomber...