I haven't but why not. It might do just fine at 77cc's. I use a 60cc Roper on my 24" mill. It isn't fast but I'm in no hurry. All I mill with it are 10" to 16" boards.
C51 should be fine for milling - chain speed is on the slow side but it should be Ok on smaller stuff. Just think of it as your first milling saw, it won't be long and you will want to update.
I have been using a Husqvarna 51 and small log mill for @12" cherry and oak. I does all right. I just got my hands on this old saw and thought it would be fun to give it a try.
It's a bigger engine and I think at 16:1 it might hold up to milling better.