Wet sumping is a pain to deal with, but my thinking’s is that we actually don’t use these machines as they were originally designed to be used. We are talking about engines designed in the 1950s which were intended to be used day in day out as transport. They never got time to wet sump to any great degree as they were always in use. Now that we only use them as a hobby they tend to stand for weeks or months without running and the non-return valve is not designed for that kind of constant use. Whilst we all would love these 70 year old machines to perform in line with modern specifications it’s not going to happen and we have to compromise/modify as best we can.
Good luck with your decision - I would fit the valve and then monitor it to make sure it is not blocking.