25% 30 year treasury bonds
His book on the subject:
A more recent book:
As in the peer thread on stock funds, this plan is not a great income generator because it's designed more for capital preservation and long term capital gains. (Unless you have half a million dollars in there and interest rates are favorable for the bonds or cash holdings.) But for me it's a great way to carve out savings and get some real compounding going. The longest drawdown in the past 40 years is 2-3 years, so I'm comfortable using it with any savings I don't expect to need to use in the next five or more years.
Implementation could hardly be simpler for the robustness that it offers. You put the money in and divide it into four parts. Once a year take a look at the balances and rebalance if any category is too far out of alignment.
For resources, Harry Browne's book mentioned in  is awesome for general investment sense and lays out the basics of the plan. Another book by Roland and Lawson  goes into much more of the nuts and bolts of implementation using different account types, tax status, and many other factors in individual situations.
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