i recently checked the dwell and timeing on my 69 404 which had a 504 motor fitted when i baught it ,it has a ducellier M48 dizzy fitted ,at idle the timeing with the strobe light is jittery [ maybe a problem with the fly weights on the advance] ,with the vac advance disconnected ,i have 3 other M48s that i can try ,firstly do these have an advance curve that is correct for the 2 litre engine ,i also have a M78 hall effects dist and a coil and ignition unit deucellier 51007 E on an alloy heat sinc , [ of a 505 posibly ] i have a colour code discrepancy between the two 3 pine plugs on the coil and igg unit ,i a;so have a two pin plug from the pos and neg which may by for a tacho ,me thinks ,if i can work out what car this electronic system if off i may be able to check the wireing diagram to work out the colour code ,but may be easier to stick with the points /condensor set up on the other distributors if the advance is compatible , and also are the two holes in the 404 bell housing still aplicabl to the 504 motor ,i have no idea which fly wheel is fitted 404 or 504 ,the timeing plate on the front of the engine has a large slot and a small as douse the pulley ,with the dowel installed the large mark on the pulley is between the marks on the engine which i have marked ,i am presuming this is the timeing mark at idle ,it seams to start /run and advance ok when set up to this mark so am leaving it at that ,,i only have manuals for 404 so am presuming the dwell and timeing is the same for the 504 engine ,a lot of variables here ,PUGS apreciate some feed back tks