You'll get great advice on here from experienced operators. My opinion is that 619 pounds is way too heavy for your tractor.
I think the ideal grapple for you would be our
50" Single Lid Wicked Grapple. It is PLENTY strong for the 3320 and other compact tractors up to around 35hp, and weighs only 274 pounds(255 pounds if you remove the intermediate slats).
The heaviest I would recommend would be our
54" or 60" Dual Lid Wicked Grapples, which weigh 349 and 382.
There are other choices out there. Keep in mind that the weight needs to be as low as possible to maximize your lift capacity.
We offer our grapples with the JD 300/400 series quick attach for no additional charge.
Shipping is free to a staffed commercial business or supporting freight terminal within 1,000 miles of Newton, NC.
Travis
Here is a video of our single lid grapple in use on a CT122 Bobcat, which has less HP and a slightly smaller frame than your 3320. It is amazing what those little tractors are capable of when the attachment is properly matched.