I've just been helping another brewer via PM on this same subject: recipe scaling.
With high gravity stovetop brewing in a small 19L pot the key figure you are concerned with is the amount of wort you want in your fermenter at OG.
That's the number you use to calculate your scaling.
If your stovetop system can pump out 16L of 1.050 in the fermenter and the recipe you're interested in is 55L, then:
Your recipe needs to be 16/55ths the size, or about a quarter, but let's get the exact number by using a calculator.
16/55 = 0.29. This is your scaling factor. All the ingredients need to be multiplied by 0.29.
Say the original recipe had 11kg of BB Ale? Multiply 0.29 by 11 and you'll get 3.19kg of base grain for your 16L recipe.
Do the same for all the ingredients. It's what brewing software does automatically, but it's helpful to understand the scaling process.