No they arent worthless....you could still use it for brewing, just let the brew cool a little bit before pumping. (say just under 200*F) Just so its not actually boiling. As for notching to fit....you can try it but why ruin a good pump head (the 809)to frankenstien it. Actually i did a little reasearch for you this morning....you can order these parts for your MDX pump:
0135-0173-1000 front housing
0135-0170-1000 rear housing
0135-0062-0100 impeller
all those parts are made of Delrin plastic and can take the higher temps no problem. We used to make a pump like this for a company that made industial coffee makers. The only difference would be the size of the impellers. Yours is actually a bigger impeller then the one above. So you would get slightly lees output then the pump normally does but atleast it wouldnt be a total loss for you.
-Walter