Realize this thread isn't quite current, but hypothetically if your FEL is 4' from rear pivot point to the point where the lift cylinder rod attaches, and 4' from there to the original pin location, and you add 5" to that distance with the QA system, you would have approximately 95% as much lift as before.
So, if your FEL is rated for 600 lbs you'd lose about 30 pounds, or 0.95 times whatever yours is rated for. This will change depending on the various distances between the above-mentioned points.
It's really more complicated than that, involving vectors and stuff - but for "kentucky windage" that'll be really close... Steve
Oh, you'd also need to subtract the weight of your added materials for the QA itself, so maybe 60-70 pounds total. Forgot about that part, sorry...