Dial up networking server?
Solution 1:
If the line between the two computers is a "dry line" as in no dial tone. You can use the following product: https://www.blackbox.com/en-us/store/Detail.aspx/Industrial-Ethernet-Extender---10-100-1-Port/LB320A
Which is called VDSL and can extend several miles at fairly good speeds, over normal single pair phone lines.