Check out the contoured dove tail offering from Ranger Point Precision. Its around 30 bucks.
Rifle Barrel 3/8 Dovetail Filler Blanks | Black Nitride Steel, Stainless Steel Options.
Marbles used to make one for Octagon barrels.
I think they offer the best aftermarket levers for Marlin and Winchester, slightly bigger, but not goofy looking like some.
Their aftermarket loading gate for Marlin lever guns is a must have for me.
Good shooting Pard.