$3100 wtf!? You could get an L67 from a yard for $500, why so much? On CL I don't see many wbodies selling for even $2500, let alone more than that for just a motor.
After you finished the top swap, did you change the oil right after, run it for 15 or so minutes, then change it again? I use cheap oil for the 15 minute change, just to clean it out. Sorry to hear about this, hopefully it'll run good after the new engine for you.