Man, your question is a kinda all over the place. So your dad wants a long action rifle, in 30-06, with a dbm? Is this a target or a hunting rifle? Standard sporter profile barrel or Sendero? Does he want the DBM flush or extended? See what I am getting at.
Lets say he has a Rem700 ADL sporter in 30-06, you can get an HS precision or B&C alaskan style stock and then add the HS precision "no smith" DBM
Remington 700 Detachable Magazines | Brownells
Same with the sendero style, can go with a no smith HS precision , or a Wyatts Long action.
Now for AI style mags, it will need to be inlett, so aftermarket stock out to CDI for inlet and bottom metal.
CDiPrecision Gunworks
The only problem with the above alternatives, is the cost of the inlet, stock , and mag will prob be more than he paid for his rifle.
Other option is to pick up a Tikka, they all come with DBM. Its a 3 round mag and can fit in his front/back pocket if/when hunting.
Lastly, Yes the 30-06 fit in the 300 WM AI magazines.
http://www.cdiprecisiongunworks.com/faq.html