I agree - 2400 appears to be a bit low for a 180 gr or even 200 gr 8x60S. I would try with a bullet lower then 180 gr first to get the speeds up and see if the bullet strikes begin to approach. If so then you have your answer. You can use lighter faster bullets or heavier and try to push them to a safe and reasonable velocity to see how close they approach. If a lighter bullet at say 2500 ft/s causes a greater cross over then als - you must go the other way.

1958 is not ancient. My 1962 vintage BRNO Super Express in 9.3 x 74 with 286 gr bullets at 2375 ft/s will always strike one over the other but about 2 inches apart (but not crossing). I know if I go to a lighter bullet the holes are closer, but 2 inches is nothing at effective ranges and I have used the rifle effectively for years this way.
I dont know if this helps, but with this rifle I cannot get the bullets to cross, light and fast or slow and fast or light and slow.....

My new BRNO 803 in 8x57 RS tho crosses right out of the box - while it can be adjusted , I am told that it is regulated for S&B 225 gr (Sierra bullets) which I have attempted to duplicate - I do see that the faster I get it (a lilttle over the S&B catelogue stated velocity), the closer the bullet strikes get, but I am pushing safety and have left well enough alone. So the crossover at 100 yds is about 1/2 inch with good solid safe loads. Given some time I am going to try the 200 gr Nosler Accubond to see how that works out.