July 13th, 1963.
I would sell the spare tyre to a tyre company for $20,000 to reverse engineer, and then go purchase a Ferrari 250 GTO, and have a garage built.
I would remove all the fluids from it, cover it up, throw in a jar of silica jel, then seal it in the garage.
Hope for the best, and return to the future.
Open the garage, inspect it, do a quick restore job and then sell it for $10,000,000 the next day.
Give private investigator some money to find Longos address, send him $1000 of sex toys every Christmas.