I believe the only difference in the stock for the shadow and the standard model 70 is the shadow has a blind magazine with no floor plate.
You could add a hinged floor plate or a removable magazine by purchasing either, and then buy a stock for a hinged floor plate model 70.
Or just order a stock for a model 70 with a blind magazine box.
Boyd's stocks has both on their website starting at about $130.00 in several styles and colors.
I have two Marlin rifles that I purchased Boyd's stocks for and the improvement in accuracy was unbelievable.
Those cheap plastic gun stocks are sometimes to flexible and cause contact where it shouldn't and allow periodic movement that kills your accuracy.
If you can grip the for end of the stock and flex it side to side, that's likely the problem.
I did glass bed the recoil lug area on the rifles I worked on , but the fit was good on the stocks I received.
Hope this helps.