Are these numbers right? *Seems to good to be true. *
It sounds like you're drawing down $20K/year savings for eight years so at your wife's retirement you'll have consumed roughly half your portfolio.
The short-term trick is making sure that your $300K is reasonably certain to survive the next eight years with such a high withdrawal rate. For example it might be a bad idea to have it all in small-cap nanobiotech stocks, but a high-bond portfolio might do fine.
The long-term trick is figuring out how to obtain $100K/year in retirement for the rest of your life. If you optimistically survive the eight years to retirement with $175K remaining (a little portfolio growth?) and then kick up withdrawals from $20K to $44K, you'll only have four or five years before you've consumed your savings. You'll still be a good bit short of SS and you haven't mentioned what happens to your health insurance after she retires.
The bad news is that if you want a survivable 4% withdrawal rate of $44K/year (rising with inflation) then you're gonna need to start with $1.1M when your spouse retires.
The good news is that you might be able to live on a lot less than $100K/year. It all depends where you live & how you live. Or you could decide how much you're willing to work now to ensure that you have $100K/year in retirement.
But, yeah, the numbers are too good to be true.