Green’s Dictionary of Slang

excellently, very well.

1796		T.G. Fessenden ‘Rustic Revel’ Poems (1804) 20: Sure Miss Airy dances topping, / Lighter than a cricket hopping.
1889		‘’Arry on the Ice’ Punch 23 Feb. 85: The year began topping, dear pal.
1912		E. Pugh City Of The World 238: ‘You don’t like school?’ [...] ‘I’d like it topping if it wasn’t for the lessons. It’s warm and dry and all that.’.