There is no great way to position them via measurement only, especially after the originals have been broken and booger welded up.
Trial fit the trunk without springs. Position gaps, tack the hinges.
Remove the trunk - weld them in place.
Kudos to you for avoiding the aftermarket bolt on. Personally, I hate solutions that add more parts and more weight to what is supposed to be a lightweight car. Sure it’s not much added weight but that is how cars get so heavy. Death by a thousand cuts. A little weight here, a little over there, next thing you know the car is 10 - 20% heavier.