I agree with Don. In the case of Porrop, it's more likely Sharp didn't know the word Porret at all, and simply wrote what he heard. So one wouldn't expect to find "porrop" as a variant spelling in the OED--it's not a variant spelling, just a transcription error!

As for the JSTOR article, I have access from my job, which is at a library. It would be illegal for me to distribute the article to you, using my Library's privileges. Best thing you can do is go to your own local library, where they probably pay the license fee, and print it out there.