I found that the threaded fitting sold with the kettle ball valve setups is too short. You need at least 1-1/2" to get through the cooler wall and into both the valve and bulkhead on the other side. You'll also want a bulkhead fitting to mate the screen to the threaded part coming through the cooler wall. You'll also want to re-use the washer that was inside the cooler over the threaded item that went through the wall. That will help you to get a better seal inside.
Here's some pic's of how I put my cooler mash tun together..
Mating the nipple on the inside (connected to the bulkhead) to the bazooka screen.
What the valve looks like outside, at least initially...
Once I got the right length fitting to mate the valve (outside the cooler) to the bulkhead inside the cooler, it was pretty easy to get it all together. I did end up using the thicker o-rings in the setup though, since I found the ones that came with the kit too thin. I've actually built a second mash tun cooler since my original, so that I can more easily mash different amounts of grain. In my 10 gallon round cooler, I can mash ~24# of grain, In the 70qt, I can mash ~44#... Means I can make a big barley wine in either a 5 or 10 gallon batch size without issue.
I'm busy in the morning with vehicle maintenance. Otherwise I'd volunteer to hook up with you then to get things figured out. I have some spare bulkheads that you could have one of. If you're up for it, head down to Strange Brew in Marlboro, MA and have Josh (he's one of the good people there) help you out. You'll probably need to get a couple of fittings, but it will be better/easier than trying to get everything all over again.
BTW, I did try to just get a longer threaded fitting from a plumbing supplier as well as Lowe's/HD and neither really worked. Better to get the fitting that is designed to work with the ball valve from the start. I'd also keep the valve made for the kettle conversion.