I think based on some inexpert googling that what Locke calls "sweet cream" is what a British person today would call "single cream" (or just "cream"). Based on comparing fat content (about 18%) this is roughly between what Americans seem to call "half-and-half" and "light-cream".
On the other hand the butter content in this recipe is bonkers. The only way that makes sense to me is if you lose a lot of butter in the process of clarifying it, which is a step in the original recipe which isn't mentioned in the translated version in the article.
I don't know how wealthy Locke was, but people generally ate less back then cause food was less readily available. Meat was more of a special occasion rather than everyday staple like it is for a lot of Europeans today.
On the other hand the butter content in this recipe is bonkers. The only way that makes sense to me is if you lose a lot of butter in the process of clarifying it, which is a step in the original recipe which isn't mentioned in the translated version in the article.