What about a Romak 3 (7.62 x 54R)? It is sometimes called a long-range AK.
Adequate internal ballistics require a very good chamber and barrel (Red Jacket used a Shilen) and a machined receiver.
Adequate external ballistics requires repeatability (match ammo) and a trajectory designed to be relatively flat. Unfortunately, the 7.62x39 has moore or less the same trajectory as a .30-30 - good for ranges out to 100-150 meters, but after that it quickly becomes a rock. The best way to judge the 7.62x54R is to pull its terminal ballistics from a Hornady/Remington/whoever ammo maker and graph the results, comparing it to other rounds that you know to be good for long range. One word of caution - Published numbers only go out to about 500 yards. I have had some luck in putting the numbers into Excel, graphing them, and then using the last 3 or 4 entries to create a trend line out to 1,000 yards. For initial selection purposes that will be good enough without resorting to ballistics software that requires numbers you won’t have access to.