There is a Kubota backhoe made specifically for the
L3750 and
L4150. The L4540 and slightly newer, L4540A are heavy duty frame mounted backhoes, with a PTO driven oil pump and separate oil reservoir under the tractor. I believe that these backhoes were made by Bradco for Kubota. I think the Bradco part number was 11HD, but the 9HD would also fit. These are Heavy Duty units, with 3" cylinders, including 3" swing cylinders instead of a chain drive to swing the backhoe.
I have an
L4150 with the L4540 backhoe, and it works very well with lots of digging power. It is very good match for this tractor, and while it won't dig out tree stumps anything like a 580K Case, it shouldn't because the unit weighs only about 1/2 as much. But it will dig out tree stumps, it just takes a little longer and it will dig a trench 123" deep with 167" reach. It is rated to lift 690 lbs at full boom extension.
The frame stays on the tractor, and actually ties in with the FEL loader frame to strengthen and support the entire tractor under carriage. The backhoe can be removed in about 10 minutes. You can then reinstall the 3-pt arms and use it just like before. Reinstallation is also quite easy, as you use the stabilizer arms to raise and lower the entire backhoe. It is secured to the frame via 4 tapered bolts, which gives it a VERY solid mounting system. About the only drawback is that the external oil reservoir reduces the clearance under the tractor when the backhoe is installed. So far it has never been a problem for me, but it is something to be aware of as it reduces the ground clearance to 9" when mounted on the
L4150.
It could be a little difficult to find one, though I saw one for sale on ebay several months ago. I think it was started at about $2k, but I don't recall what it sold for.
A 3-pt hoe would also work, but in general, they are very small and light-weight when compared to the Kubota L4540/Bradco hoes. The buckets are generally much shallower (don't hold as much material), the cylinders are usually 2" or 2-1/2" and the dig and reach are considerably less. But it depends what you want to do, and the type of soil you will be digging in.
Hope this helps