I removed a OEM oil cooler off a mid 80s 360 Diplomat cop car. Cooler fed from oil pressure sender port rear top of block and flowed thru cooler in front of radiator. Oil out of cooler dumped into the timing chain cover by way of a banjo bolt on the fuel pump. I'm sure cop motors had a HV oil pump. IIRC the lines were 5/16" ID. This oil flow path would not send all pump output thru the cooler so smaller diameter lines would work.