This was severely rusted up so I tried the vinegar treatment on it and was surprised to see the 375.
Found one on the wrenching news to match it,
Marseilles MFG Co./Deere 7 1/4" Tee wrench.

Nice find, rare wrench even in that condition.

Should I try to clean this further? It still has numerous hunks of caked rust on it.

If you think the rust will continue to eat the wrench, you probably should. Otherwise I wouldn't, but at this point this is a wrench that probably needs to be coated or painted or whatever floats your boat along those lines. Or you can just sell it to me...lol

That's a "lucky dog" find there. Poor shape or not.  Good job.