Hi noramime,
You're right, sputum test is 60 days; usually yung additional test for lungs sa Canada PR visa medical adds 3 additional months to repeat the chest x-ray.
Call the clinic where you plan to take your medical, but when you get the nomination and ITA, I think you can proceed with the preliminary tests, and you can also give your medical reports on the ongoing treatment...you can get a UMF and it may be regarded "incomplete" pending the additional tests (if ever they are requested), but at least you'll be able to send your PR application na with the UMF.
They'll ask you when was the last time you had a chest x-ray, and I think they'll only ask for it if you have the old-style film, but not digital.
If you decline the OINP nomination to buy more time, you will have to ask OINP to resend it to you...actually, I don't know if that's possible for the same EE profile, or they will ask you to create a new EE profile if a provincial nomination was previously declined.
But I think since you are already undergoing treatment, you can proceed with the medicals after accepting the nomination and ITA once you get it. Just show up to your medicals with original reports of your treatment and explanation of pulmonary fibrosis, specially if the scar will still show up in the x-ray...they will attach it to your e-Medical file, and ideally, they won't ask you to take the 3-month test anymore.