Emulsified oil in the rocker cover was common on older engines in my experience and not necessarily an indication of a problem requiring investigation. Particularly the 1725 ally head, BL "S" series, and to a lesser extent BL "A" series, "B" series, and Ford Kent amongst others. The problem is caused by the rocker cover not getting hot enough to evaporate condensation. My engine takes about 47 minutes to get the oil fully up to temperature on average (ambient temperature affects). Unless you are losing water I wouldn't worry.
Scrape the sludge out every 5000, or avoid short journeys, or do what BL did on the "S" series and wrap the oil filler and cam cover in insulating material to help keep it warm...
I find using a modern oil helps too. I use 5W50 fully synthetic racing oil in my engine. I could explain the logic but it is a long read. Not a sign of any milky deposits in the rocker cover for years.
I will wait for someone to criticise use of synthetic/semi synthetic/5W etc before I dig out the science...