Re: neck and body mismatch
My understanding of it is this:
F = Fujigen (the factory it was made in), then if it's pre-'97 (or '96?), the first digit signifies the year. After '97, they changed it so that the 2 digits after the F signify the year of production. The remaining digits tell you the production run, so my own guitar, an RG750, for example, has the serial F041830, which means mine was the 41,830th guitar built in the Fujigen factory during 1990.
If I'm wrong, someone feel free to correct me. If Guitarslinger is right in that the number denotes the month too (he probably is), then mine was the 1830th guitar produced at Fujigen during 1990 and it was made in April of that year. This to me sounds more realistic, but if someone can clarify, I'm interested to know.