300-790 USD
100-400 USD
You will have to contact FN to find out.
$100-$400, depending on the exact model and condition.
139791
25-250 usd
Not with just the serial number.
1959.
Which model? The 1910 or 1955? Go to the link below.
There are several: AR4 LR308, Armalite AR-10 A2, Remington R-25, POF-USA P-415, Barrett REC-7, Knight SR-25, Stag Arms M-7, DPMS .308 Mark 12, Fulton Armory FAR 308, FNH FNAR 308, FN SCAR 17S, LaRue Tactical PredetAR 7.62,and the FN/FAL Umbel 7.62 Battle rifle.
It's just a carrying handle, same as what can be found on the FN FAL.
without more of a description it could be 10-1000 USD
7.62x51. Some early production rifles for Venezuela were manufactured in 7x49, but were later converted to 7.62x51.