90% would go into the index fund and the other 10% would go into treasuries. Keep It Simple Stupid!
The last thing that your heirs need to deal with is a complicated estate plan while they're grieving. Obviously they're free to do with it as they please when you die unless you set it up in a trust, but if you "trust" them then this is a pretty good plan.
If the person enacts the 3% rule as I've previous instructed than they could quite easily live off of the 10% treasuries for 4 years while the stocks appreciate and while you also get dividend income. There's no guarantee that the stock market will be higher in 4 years, but there's a pretty good chance it will be.
Ideally you'd want to be in a situation where the heir can live off of the dividend income exclusively for the rest of their life without ever having to touch the principle. Take a look at the website firecalc.com to see how much you need to virtually eliminate the possibility of running out of money.
For instance, I would need to accumulate $1,100,000 in order to live for 60 years and not run out of money. Assuming my current spending rate of $36,000 per year. What's yours and what would your heir need?