the weight would definitely help most decide on authenticity. does your coin have a lettered edge? Had to check myself to make sure it wasn't a denver mint coin. wowsers on that 27d $20 not that yours isn't necessarily drool worthy but sometimes a tiny letter makes all the difference.
My first thought as soon as I saw this was that the overall look of the coin was not right. take photo of edge and get a weight on it to ensure that it at least passes those two tests so you don't waste your $ sending it off to a TPG
I hope it is real, but from the pictures side by side The stars on your inherited coin look a bit mushy above the word Liberty, and the bottom of the torch looks pointier than the graded coin. The whole coin looks very soft.