Ok, been working through this recipe since maraschino has been available in my part of the world for the first time (3 separate attempts)

First and foremost- this version is ultimate when it comes to ratios. No question.

Using pink pink grapefruit fresh pressed makes all the difference - the only improvement I think I can bring to it is to use granulated sugar instead of syrup (trust me, the slight difference in dilution is noticeable); my preference for aged rum (Havana Club Especial, 37.5%) while watching the 50’s version of The Old Man And The Sea might be a bias.

The only thing the site could use at this point is a way to calculate a half recipe. Because some users may start writing a novel after only 2 iterations.

To add to Simon's comment, I think the egg white lends itself well to wash out the drink with extra dilution (with a non-flavoured ingredient), not exactly in order to have foam. I'd do a straight wet shake for this reason