Similar situation to Irelephant, first I'm reading about Loforo. Doing some brief research, it doesn't look like Loforo's integrated ActivityPub that much, nor does it seem to be open source so others could run their own instances.
In those respects Wafrn is the clear choice for a federated Tumblr-like, as it's open source and integrates ActivityPub thoroughly. As a matter of fact, a little more digging and I found where someone has been helping test run another Wafrn instance in the form of "evil" Wafrn.