bill,
not sure if this helps this guy has some stuff adapters and he says he has the reduction boxes too.....i'll be passing by tomorrow and wednesday so if you find something or talk to him i can pick it up for you....
http://cgi.ebay.com/ebaymotors/Chevy-TH400-to-NP203-Adapter-TH-400-NP-203_W0QQitemZ160370198205QQcmdZViewItemQQptZMotors_Car_Truck_Parts_Accessories?hash=item2556cf06bd[url=http://cgi.ebay.com/ebaymotors/Chevy-TH400-to-NP203-Adapter-TH-400-NP-203_W0QQitemZ160370198205QQcmdZViewItemQQptZMotors_Car_Truck_Parts_Accessories?hash=item2556cf06bd]