I read that H and H made some Magnum 98 actions [that is cutting a standard length 98 action, and lengthening it ] also someone in the U.S made a about half a dozen that way .
There is info on shortening actions ,but not much to be found on lengthening them ,you would need a competent gunsmith, and one who is willing to do it ,who knows what he's doing e.g welding ,heat treatment etc .If I could find someone ,its something I would like to get done ,rather than paying the 5k and up prices for a Brand New action .
Would need ideally two actions made by the same manufacturer and in excellent condition ,and or two recent production actions .