The search terms I've used on google:
Praktica L service manual; Praktica L repair manual; Praktica L IPB; Praktica L parts diagram.
I don't think one exists but if it dies a factory authorized service shop still open for business might have one.
The exploded view exists, within the official repair manual. But in the only pdf file online, those pages missing; and a photo on the net of these pages is not readable.
Earlier this afternoon, as I was reviewing my old reference pictures, I accidentally found the proper way to remove the lens mount plastic ring.
Inside the mirror box, there's a slot which gives access to a hole that goes through the mount. Using a small curved pick and a reasonable level of forces, the ring can easily be pushed out.