Fully restored would have put a 289 in it, but the 302 shouldn't hurt you too bad on the value. Just off the top of my head, depending on how well the restoration was done, average price would be $20k-$25k. More if done really well, less if shortcuts were taken. I would suggest contacting a couple classic car clubs in your area and find out where you can take it for a proper appraisal (will cost you about $75).
Well the Mustang craze is mellow right now. but it being a fastback does advantage the deal..... If you are looking to price it look at Hemmings motor news or a vintage car restorer there are people who will give you an idea of an asking price for the car. but hemmings is where I get the market values for my restore projects I then don't move from that price as they are worth it..
What Dragnet, and Andy both said are true. The market is soft right now, and it would be worth more if it was a numbers matching car. If you had the restoration done you will not get out of it what you paid to have it done. Being the owner of a 1966 fastback, I would say you won't go to wrong asking 25K. I have a friend that just sold a newly restord 66 FB for 30K.