Those add to 80%. I recommend an international component, it will be a better diversifier than another slice of US company stock. Not less than 50% stock, not more than 50% US stock, 10-40% bonds (depending on availability of social security, willingness to take risk, and other factors), feel free to swap real estate in as desired.
$500k is large enough that DCA could start to make sense. Of course there is no good time frame to do it over, because the odds are that you will end with less money than if you had invested all at once over any time frame. You are sacrificing a better best case, a better mean case, and a better median case to get a better worst case. One year seems ok, or 100 weeks, or whatever. Not more than two years for sure. That said, at 52 y/o pretty soon this asset allocation will be fixed for life and there will be no opportunity to DCA. If family person is able to live with that allocation for the next 40 years, what is so scary about the first 2 years? You could be looking at a "poor allocation problem" rather than a "dollar cost averaging problem."
It's getting old but my favorite investment author has a guest post which concludes one year is the optimal period.
http://www.efficientfrontier.com/ef/997/dca.htmVanguard deposits default to Vanguard Federal Money Market Fund, which is consists of US government debt maturing within 90 days.
If you decide to DCA, be certain to automate this process to prevent yourself and others from screwing it up.