Gotta agree with most guys on here, decide what you want from the car, and then build it. Sounds like you want to flip it, so that period-correct Hemi is probably gonna be your best bet. Whether its worth the price tag to you? Depends on what you paid for the car i suppose.
Took me 4 years to get my hands on my car. After following auction prices on sites like Mecum and Barrett Jackson (because I live on the other side of the world), a few patterns started to emerge in regards to price. I wont go into detail, but once you decide what it is your going after, a fairly accurate price gauge can be had.
Personally, I love the 68. But after deciding how much i wanted to spend, it quickly became apparent that I wasn't gonna get my hands on something with a matching #'s engine. So while I was at it, it might as well have been an upgrade in CI. Im happy with my purchase and my car, and I'm sure that whichever way you go, someone is gonna be real happy with your car too.