+1 to the Boglehead link. It might also be useful to read this:
http://www.bogleheads.org/wiki/Three-fund_portfolioPersonally, I do something like this: 49% US stock, 33% INT stock, 10% bond, 5% REIT, 3% Other. The last two are entirely optional, though.
So if I were doing that in your 401K, I'd do something like:
Vanguard Inst Index 50%
Vanguard Total International 35%
PIMCO Total Return 15%
I don't love PIMCO, though, but I'm not familiar with Putnam Stable Fund, so I can't speak to whether or not that's a good stand in for a bond index fund. Truthfully, if I were you, I'd just do the two Vanguard indexes (60/40 or something like that) in the 401K and get a bond index with a lower expense ratio in your husband's IRA.
The key (as I understand it) isn't picking the right "magic number" of percentages, it's picking a balance and sticking to it (meaning, rebalancing as needed). As far as 90 vs 180, I'd probably do 180, but I think either would be fine.