That’s an interesting question! There is no way to change pixel aspect ratio (I believe that’s what it’s called) in Figma. The only solution I can see here is to use an oversized grid with 48px columns and 61px rows (or vice versa). Then you have to make all of your objects about 50 times larger to fit this grid nicely. And then do some multiplications in the W and H fields to make sizes correct (e.g. this “button” is 100w and 24h — I multiplied 100 by 48 and 24 by 61).