Having been down this road...
Find a gunsmith you want to work with and work through him. Would you act as the general contractor building your dream home if you knew nothing about construction?
I've done both ways with the actions. Getting a Stiller Tac300 is probably the best way to go. Better than a reworked 700 and less expensive than a full blown custom.
Good luck and have fun! Also, tripple your expected build time and double your budget
You'll have a lot less stress and feel better when it's over!