Flip the stock upside-down and lay just the forend tip itself on the anvil section of your bench vise (or another dead hard surface).
Hold the stock steady with one hand and with the other, take a few carefully aimed and placed wacks onto the plastic forend tip w/a decent sized hammer.
The elderly Bishop plastic product will crack and break into pieces for you.
Leaving you with what was used to attach it to the end of the forend wood.
Might be a single dowel in there,,metal,,wood who knows.
Pull it out from there.
Might be two or more 'pins' made from nothing more than common nails all glued together at assembly time.
It all depends on how the tip was constructed (solid, hollow, cast w/a threaded fitting, ect).
Save some time and over rated excersize hacksawing and just crack it and take it off.
Pull any fitment hardware, then proceed from there with your new tip.
You can use a Winchester M70 checkered steel butt plate. They are still avail at about $60+,,probably less if you hunt around at shows in the parts boxes.
I have found them in less than stellar shape for considerably less and used them for various projects.
One ended up as a smooth shotgun style plate on a '94
Slight arc can be straightened if you want by heating red and simple forging from the back side.
Or refit the rifles stock to fit the Winchester M70 butt plate.
Flea-Bay might always be a source I'd imagine for a cosmeticly challenged plate at a reduced price to work over.
..and then again sometimes not the way auctions go.
Those plates were used on everything from the M97 to the 71 to the M70. So there are quite a few around.
Good luck on your project. Have Fun!