Kristi,
1. Find a reputable qualified instructor to provide transition training and tail wheel endorsement in your RV6 (If it's deemed safe and airworthy).
2. Schedule training.
3. Obtain and review training syllabus.
4. Attend training as scheduled. If identified standards are met > receive TW endorsement and transition sign off.
5. At the completion of training, after receiving the endorsements, ask the instructor to provide an evaluation of your cross country capabilities in the RV6. Inform the instructor you plan to fly the RV6 from Cali to NY (or where ever). Discuss routes and possible alternatives, WX and other factors such as range fuel stops, over night stays and lay overs. Have the instructor evaluate the PIC ability to make the flight alone.
I recently did the above steps. Took my transition training with Mike Seagar in his RV7 in Oregon like so many others on this site. Mike by far is the best and most patient instructor I've flown with.
Around 85 days later, I picked up my RV8 in Arizona and practiced there for three days allowing the WX to clear in NorCal (yes it actually rained once this year). All by myself, I took it slow flying from Benson AZ to Redlands CA the first day with a stop in Blythe to sort out the airspace over Palm Springs.
The next day I flew (alone) from Redlands to Cameron Park CA.
Your PIC should be able to accomplish a cross country flight from Concord to the east coast (or anywhere else for that matter). Only the PIC can make that decision.
Best wishes to the PIC. He's going to love owning an RV. I sure do.