Sounds like Vacuum Advance in hooked up to full vacuum port .[Driver side port ] Need to be on venturi vacuum port [ Passenger side lower front Small Port] .You get full advance at idle and , lose advance when at Part Throttle & Wide Open Throttle !
I Custom Build 727 & 904 TF Trans . I am in Greeley Colorado . Where do you live at ? Freight can be high $$ . 727 Weight is 135 Lbs . Without Fluid and Converter .. Street or Strip and Describe Engine ..