That mod looks like it will really help your lift capacity.
I have a L3400 that doesn't have a QA as they were released shortly after we bought it.
While I don't really have an interest in using multiple skid-steer attachment, I would like to switch over to forks, bucket-less. I hadn't really checked out the ATI pin-on conversion until I looked at your pics.
Are you happy with it? Do you remember roughly what it cost?
I like the ATI unit a lot .. I can change from the bucket to plow or forks in less then 3 min.,, It's very easy.. I think it cost about $250 or so ..
.I don't know, I think if it were me I'd add some cross bracing. The tube isn't really that heavy and I'd be worried about torquing one of the FEL arms. When you have a bucket or other attachment on, it provides some torsional resistance to keep the arms from torquing.
Then again, I do tend to overbuild most things..
I only plan on lifting pallets of wood and once and a while to pick up brush .. hmm and to lift the Harley s into the workshop in the fall.. Maybe I will look at bracing.. 14 grand 3' in the air roiling off the pallet... ya I'll look at that again.. you might be right bikerdib..