Egg sizes of yesteryear and today
There is no absolute conversion as egg sizes were not standardized back then.  For the USA, not England, the food timeline http://www.foodtimeline.org/foodeggs.html under the section "Egg sizes the USA" (about 1/10th of the way down) starts with (bolding added):


  What size hen's egg was used to make a cake in the 1840s? Excellent question with no simple answer. Today's consumers find eggs clearly marked with quality grades in different sizes. In the 1840s, many consumers found eggs under the chicken in the family coop. Pre-industrial American cook books regularly acknowledge the relationship between fresh eggs and best product but are silent on size. Cook books focus on identifying "good" eggs, proper storage, and preservation techniques. In those days, the size of chicken eggs depended upon breed, feed, season and cooping conditions.


Recreating old recipes with modern products always poses special challenges. When eggs are on the shopping list, think small or medium.

The section continues with various extracts describing approximate weights and other commentary.

From the above, I would go with Dorothy's comment and use medium, starting with two or three and adjust for consistency.  Don't forget to weigh what you use so that you can repeat your success with any eggs.