I had 2 Thiele cabs,both loaded with M.B. 90's. So I swapped out one with a vintage 30....sounded thin,alittle high end shrillyand not as tight on the bottom . At that time I was running a MKIII E.V. loaded combo and a open back matching umbinga 1x12 E.V. cab. I bought the 2 thieles to get more bottom end. It did work...but the Celestion Vin30 swap I did...'thumbs down". I wouldnt pass on swapping yours out if you have the 30 laying around,but if your going to buy one..well,I told you what I found.Oh,I did like the sound of that cab with the 30 in it...when I pulled 2 tubes out of the MKIII and put in only 2 EL34's. But since I didnt play out with the amp in that configuration(only used 4 6L6's in it live) I found it a bit more or a "bedroom"amp thing.
Good luck