As I commented on What Would You Do Without Morality?:

I expect I'll keep on doing what I'm doing, which is trying to work out what I actually want. [...] So far I haven't lapsed into nihilist catatonia or killed everyone or destroyed the economy. This suggests that assuming a morality is not a requirement for not behaving like a sociopath. I have friends and it pleases me to be nice to them and I have a lovely girlfriend and a lovely three year old daughter who I spend most of my life's efforts on trying to bring up and on the prerequisites to that.

Without an intrinsic point to the universe, it seems likely to me that people would go on behaving with the same sort of observable morality they had before. I consider this supported by the observed phenomenon that Christians who turn atheist seem to still behave as ethically as they did before, without a perception of God to direct them.

This may or may not directly answer your question of what's the correct moral engine to have in one's mind (if there is a single correct moral engine to have in one's mind - and even assuming what's in one's mind has a tremendous effect on one's observed ethical behaviour, rather than said ethical behaviour largely being evolved behaviour going back millions of years before the mind), but I don't actually care about that except insofar as it affects the observed behaviour.