Facebook has a very good page dedicated to the HU-16 series, I won't post the link here, so contact me with a DM or send me a PM and I'll tell you how to get there. I'll get back to you later on it.
The page owner is good friend and I'm an Admin, he has a digital copy of several HU-16/UF-1 Operating/Maint. manuals and can answer just about anything on it.