I'd put my PE stamp on it.
I'll put it this way, building a stand for 800# out of 2x4's is comparable to building you house out of 12" wide flange I-beams.
Can it be done?....yes
Do you need to?....no
The pages that give you plans just do one thing, overbuild. I guarantee that the people that wrote those pages really just slapped the stand together. Nothing more....no calculations.
If consequence dictate my course of action, then it doesn't matter what's right, it's only wrong if you get caught.....