I'm changing my 870 wingmaster from a hunter to a home defence weapon. It was made in the late 60's to early 70's and has a 2 3\4" chamber. I have an 18 1\2" barrel and magazine extension on order. My question is this will any pistol grip forend for an 870 work on this older shotgun? Has there been any changes regarding the forend of the 870 in the last 40 years? Thanks for any advise.