I just bought a Mahindra 509 for my 3510. It weighs 1500# without the subframe. Your 3510 should carry the unit. Just looking at it, I would guess at least 20 HP+ to power it. A FEL and loaded tires will make it more stable.
All the research I did before purchasing suggested to use a frame mount to prevent tractor damage, which due to my needs was a must. My needs require a stable mount for serious digging and excavating plans.
Your needs and amount of money to spend will dictate whether to use a 3PT mount vs a rigid Subframe mount
Sometimes a good deal turns into a expensive deal that's not so good.