Use an authentic tasting distilled old tom gin that's balanced rather than overly sweet and you'll have a fabulous cocktail.
We've used dry vermouth to balance the sweet vermouth but if you're looking for simplicity and less ingredients then you might want to omit the dry vermouth and balance by reducing the sweet vermouth and maraschino while also doubling the bitters as follows:
2 shot Old Tom Gin
2/3 shot Sweet vermouth
1/8 shot Maraschino
2 dashes of orange bitters