Sell my Duster or 360 Swap??? Help?!?

Yea, you would pay a lot more than $2,500 for a Duster 360 that is in nice of shape as your car now. I paid a lot more than that for mine and the work that needed to be done wasn't even finished.
If your car is in good shape like you say, I'd keep it and do the V8 conversion. It's not that big of a deal. IMOP. Good luck...