Where in Pa?  I used to do some "cob chop" with a 1640 and then a 1666.  Run rotor at 1000 or 1100 rpm, and concaves closed all the way.  As far as the chaffer,  you can maybe get away with running with no sieves at all or if you can find a cheap chaffer sieve you can cut every other louver out or I have seen special made sieves with big holes cut in kinda like the plywood idea above.  No matter what you do for a top sieve the shoe sieve will need to come out.  I think I used to run the fan kinda slow, maybe 700 or so. Next issue is getting it out of the bin......you will need to modify the cross auger covers in some way.  I think what I did on the last machine I used for this purpose was just to raise the auger covers by maybe 6 inches in order to let stuff fall in.  Really high moisture cob chop does not have good flow charactaristics. Have fun.....