Be careful with how much weight your putting on that front axle. If it was right over the axle that's one thing but with that weight that far out front it's going to put a lot more strain on the front of the tractor. I have mine set to lift 400 hundred pounds. If I were to drive into a rut or hole the load would momentarily increase dramatically. I have a cast iron front axle on mine and so far it hasn't been problem. Your tractor could be built a lot heavier than mine though. Just something to think about.
It's fun watching your project come along.
Truth be told the hydraulics on the Kwik way loader has a max pressure setting of 400 psi and I will be setting it there when the time comes so that will be my limiting factor. If it picks up 500 lbs then it does, if it's less then so be it but I really don't want to go above the 500 lbs.
I'm not naive enough to think this little loader can do the job of it's larger cousins. The Gravely/loader should be plenty heavy duty enough for the jobs I have in mind for it, mostly whatever I'd use a normal sized wheelbarrow for with the occasional heavy lift.
I will be converting my very small backyard into a patio about 40'X40', the loader will make that job a little faster than hand digging the topsoil out and moving the patio materials in.
If you haven't yet, check out my thread on my 816 GT. That will give you an idea of how heavy duty it is.