How can you ask some one to make a new deal 5 month's later should have taken some one with you to look at the car if you had any kind of doubt.
Those vette's are hard to get and are worth a good deal of money even basket case's bring good money but even with all that you made a deal 5 month's ago sounds like you own the vette to me i wouldn't even call some one back after i made a deal it is mine then and i own it regardless what it is worth i guess one question you should ask your shelf would you change the deal 5 months later if the shoe was on the other foot Probably not .
I don't know either person here but sounds like to me you just need to stand up to the deal you made and go on with your life.