The 4672A backhoe you've got pictured is an older Kubota 3 point model from about 1990-2003. That one pictured looks brand new, by the way. Here's a link to the installation manual for that BH:
http://www.kubotabooks.com/AutoIndex/index.php?dir=Backhoes/
The 4672 was meant for the smaller B series tractors made in those years. I suppose that means technically it wasn't recommended for the L models. Would it fit on an L model from those years? Don't know for sure, but being a "3 point" type hoe, there's no subframe so it might work, maybe with some tinkering needed. Would it fit your L3301? Same answer.
A lot of owners have used these Kubota 3 point hoes with success even though they are not meant for really heavy backhoe work and do put extra strain on the tractor since there's no subframe. But it says something that Kubota no longer offers 3 point backhoes.
There is an important paragraph in the manual that explains, "Tractors that receive a B4672 or B4690 Backhoe require the installation of a Reinforced 3-Point Top Link Bracket." Don't know if that also applies to your newer L3301, but highly recommend you find out before proceeding. A 3 pt. backhoe places extraordinary strain on the tractor rear end, in case I forgot to mention it.
I wouldn't worry about the small size of this backhoe, but if it were my tractor, I'd find a full subframe model instead. Just one guy's opinion.