Usually they have 1:14" twist in a 458 Win and 458 Lott. What happens if they use a twist of 1:18"?
Do that 1:18" twist that the rifle shot badly?

Is the Ruger No 1 a good choice to build a 458 Lott on?

the 1-18" Twist would probably be a little kinder to cast bullets than the 1-14" twist. I cannot say whether it would shoot well with the normal .458 bullets or not though.
BTW, Ruger is making the #1 in .458 Lott this year. If one is not available in Sweden in that caliber then I would say that as long as you had a #1 that originally was chambered for a belted mag then it should work fine. Sean