On later serp engines it is on top of the inlet manifold, nearside, in front of the number one injector. It's the thing with the blue and yellow wire coming from it, by the corner of the fuel rail. Have you looked there?
Thanks QBee, I can't see it on my preserp so maybe they were different in that area; I thought it was only in the front cover area and oil pump drive where the differences were but what do I know, cheers, John.