Used one of my favourite witbiers - Gulpener Korenwolf. It's definitely more of an upgraded beer than a cocktail. If I came at this from the pov of a whiskey sour with wheat notes I would be disappointed; as a wheat beer with a nice orange and bourbon note? excellent.
IDK why you’d bother…too little beer and all you get is a typical bourbon/lemon cocktail taste…too much beer and you get neither beer as a flavour nor the bourbon. (Full disclosure: I used Erdinger Dunkel for my weissen beer.)
A Dunkel is definitely not the right choice for this cocktail. I'd go with a hefeweizen or a Belgian wit, something lighter that will pair better with the citrus notes of the lemon and marmalade.