As with some other words, like pravi, provi, provi, the case of verko and vorko make morphologically apparent a semantic link with a vowel change, as it often occurs in Semitics languages.
So, I would translate verko with work. That's probably the closest single word counterpart, although the semantic fields of each term greatly differ. Now, I recently discovered vorko, that PIV define as Grava konstruaĵo (aŭtovojo, ponto, tunelo ks). Is their a better suited translation than work for vorko, so one might translate a discourse containing both verko and vorko in English?