OK, I have an 8N and I need a ROPS, but many of the forums discussing these are a bit long in the tooth. So here's an update based on a lot of looking.
I wholeheartedly agree that if you can afford it, you should by a professionally manufactured ROPS. The variables of workmanship and the liabilities involved are huge. Having said that, those of us with an 8N that does more than just go to shows usually need a cost-effective solution.
After combing through many sources I've found 3 solutions, all of which have been found by others, but I've gathered them here in one place.
1 - Hercules ROPS - http://justtractorparts.com/rops.aspx About $750 for the 8N model shipping is another story. I last spoke to the dealer in Apple Valley CA a few years ago, and he had at least one in stock.
2 - Bare-Co - http://www.bare-co.com/files-rop-rop1 Similar price. Emailed today, got a response today, through a dealer in Shingle Springs CA.
3 - NIOSH CROPS Project - https://www.cdc.gov/niosh/topics/aginjury/crops/ Full detailed plans for a DIY ROPS, professionally engineered and tested. Designed specifically to be fabricated and installed by the do-it-yourselfer, you'll have to price the steel yourself to get an idea of what the project will cost. Only has 2 brackets that need welding, the fabrication shops that do that would probably charge a mighty reasonable price. Be warned - if you go to the site with your phone or tablet, you may wonder where the hell the plans are. Go there on a PC, something wonky about how tables display.
So there it is, in one place, I plan to copy and paste this message where I can. And I plan to build the NIOSH CROPS.