They are very easy to make if you already have a donor hitch. And even if you dont, just get the 2-1/2" tube at TSC.
The part that concerns me is you question how trustworthy they are and that you will be pulling alot of weight. We dont know your back ground or your welding skills or what material you are using.
They can be made poorly and out of undersized steel and fail. Or they can be built properly so that you are more likely to pull the hitch arms off the tractor before it fails. I have made 4 or 5 of them IIRC. Two were not made with a donor hitch, rather an insert tube from TSC that costs ~15-20 bucks. And they are all built heavy enough I dont worry.
And when you say "alot" of weight, you should define that. "alot" is different to everyone. And I see you only list an 8n for a tractor, which isnt capable of pulling "alot" in the way I define it. Maybe 5k max on a trailer. And ~2000-2500# drawbar pull.
Another note: if you do build one. Make it so that the toplink is parallel with the lower links. This will allow the hitch to stay level when raising. If not, the hitch will rotate when raising and lowering, which isnt the best thing for a ball hitch and trailer.