Good start so far.
Before you weld it together you want to make sure the vertical part for your top link to hook to is the correct length.
Ideally you want your top link to run paralled with the lower arms so when you raise and lower the 3ph, the hitch stays level.
So if you measure where you're top link hooks to the tractor down to where the lower arms hook to the tractor, you want that measurement to be the same on your hitch.
This is the best pic i have to try to explain it. A should be the same as B