Tuning New Shooter Old FWB 300S

After years of not shooting, I decided to try air guns. I figured I’d buy a springer as I didn’t want to deal with air tanks and pumps. I debated about buying new versus old and decided I’d go with an FWB 300S. A few months ago, I bought one (mid 1970s) that has been sitting for years. The 300S appears complete but came in two pieces (barrel/trigger assembly and stock).
1- Where can I find an owners manual for assembly and torque settings?
2- Who do you recommend for a rebuild in the NorthEast or in the US?