I only have knowledge of Ñāṇamoli's translation which is not available for free. Does anyone have knowledge of an English translation available for free?
The Pali Text Society is about the best authority for English translations, and they did produce a reference text in 1977. There is not a lot of online translations, but here is a link to the digital version of the book:
You can try to find it at http://tipitaka.sutta.org/ , not sure about the quality of translation.
This book claims to compare The Nettippakarana and Petakopadesa, compared - xiii. 6. Authorship and ... Glossary (Pali-English). 288 ... The book here translated—as it stands, it was perhaps composed ..... The only extra source available is the contents of the two books.
This is a free resource. Hope that is of interest