Having done the "customize a mauser" thing, and spent $2,400 and two years, and ended up totally unhappy, I would very respectfully advise that you buy the Howa action as suggested. Unless you are an expert machinist who can do his own metal work, you will not save any money whatsoever trying to "customize" a military action (unless you want to just take a good 98 Mauser in 8mm, leave it in that caliber, and cut it down and clean it up, adding only a dayton traister safety, turning down the bolt handle, and drilling and tapping.)
Do not use a K-98 action, unless you leave it in the original 8mm. Towards the last three years of the war, these were being made by slave labor (intent on sabeutoge when possible), in factories that were being bombed day and night, and during periods when the Germans themselves were trying to make them quicker and cheaper. There are just too many safety issues with a K-98, unless you get a nice pre-War k-98. If you get a nice pre-war, then you would be very foolish to cut it up or re-work it. They are just too valuable.
Hope this info helps.
Big Paulie