for the moment it appears that the trouble has been the radiator fan. i've almost never seen an electric motor slow down v die completely. i'll be testing the system again today but i've had some interesting surprises along the way.
replaced all hoses and a new radiator. i may try reinstalling some of the original parts again since for instance i believe the new thermostat is not calibrated as accurately as the one i took out and i'm curious about the performance of the orig radiator since it seems as spotless internally as the entire system and i can't figure out why it might have reduced performance except that the fins might have an oxidized contact to the tubes which would reduce the heat transfer. i'm tempted to reinstall the old radiator for a test and put the new one on the shelf for the coming rebuild.