Twist and bbl length depend on what you want to do with it.
Very fast twist for very long range bullets for big game. 30" bbl would maybe be a schoche bit too long for that cartridge. Be careful with powder bridging. The RUM shoulder may reduce the probability of powder bridging but I'd start out w/ball powders just to be save.
I think that a better choice, if you wish to stick w/the standard RUM case, it the 7mm RUM. No bridging problems. Good selection of heavier bullets, including WC 200s. Twist would be something like 1-7 as w/the 270.
Just a thought......