If you are going to weld, less is more, don't worry about the depth as much as the alignment. There is plenty of wiggle room for the long nut, we will call it, to go down into the center piece without interfering with anything, but you have to make sure it is correct left/right or else the can will sit at an angle and not seal. I would suggest in this case to get some Dirko and as messy as it is use that along with the o ring to get a good seal. DO NOT GET THE DIRKO INSIDE THE CAN, but on the outside it might look bad but will seal. Set sit 24 hours after assembling before testing to make sure the Dirko dried.
Bob