It was manufactured by Mossberg. It is probably the model 353, and parts can be ordered atwww.havlinsales.com. The reason I am not certain is that there does not appear to be a written list for this cross reference.
The Western Field M854 shotgun was manufactured by Mossberg for Montgomery Ward. Mossberg produced a variety of firearms under different brand names, including the Western Field line, which was sold through Montgomery Ward stores. The M854 is a bolt-action shotgun, known for its reliability and simplicity.
You need the services of a gunsmith.
use a saw and chop the stock, then refinish and attach buttplate.