Converting any standard caliber rifle to a magnum requires the bolt face be opened up for the larger diameter casehead. Also the extractor will have to be refitted and the feed rails altered to feed the larger diameter and longer rounds. The bolt handle would need to be altered to clear a telescope mount but not for the caliber conversion. The barrel would need to be threaded and chambered to the caliber of choice and contoured.. Usually the safety has to be changed to allow operation with a scope mounted and the action would of course have to be correctly drilled and tapped for appropriate scope mount bases. There is still the finish work(polishiing, bluing, beadblasting, etc.) of course and the stock work.. As for the turned down bolt if it protrudes from the side of the bolt and then bends down it is likely a military bent bolt action. A bolt modified for a scope mount usually protrudes less than an inch from the bolt body before turning rather sharply down.