Fuel??timing ??or both??

Multiple problems.Deal with cooling first.Where is your radiator from the other car? You are asking a lot,for a stock 318 rad to cool a 400+ stroker .Is it at least a 3 core radiator?.As for the idle/ die situation,possibly a plugged idle circuit.Cheap ,to pull the mixture screws out.Then,blow out the screw holes with a rubber tipped blowgun.After that,possibly rebuild time.