The GLS is the carb engine and was later called the GL.
Being 1983 it won't have the big black bump strips but nice thin chrome ones.
If it has a sunroof then chances are it's broken or will break very soon due to weak plastic clips.
Rust around the wheels arches, sills, boot and the valences are the main spots to go.
But it's a lightweight Volvo with a redblock, don't bother asking about it buy it
Value for the 300 series us all over the place really but if it's on sorn and very good condition then I'd pay £400-£600 and if mint up to £800 but as I say that's what I would pay others will say differently.