Bone Stock 64 Malibu Conv

[oldguy64malibu]

Hi,
From Fairfield Harbour, NC.
Recently bought an all original 64 Chevelle Malibu Convertible. It is in pretty good shape , no rust issues. It has a 283, Powerglide, power steering, standard brakes, 2 barrel and dual exhaust.
I don't like the 2 speed Powerglide and wouldn't mind a little more power and better fuel mileage that a newer engine/transmission could provide. I would appreciate your suggestions on what might be the best way and easiest way to go at this. I want to keep the bench seat. Also, I working on a retiree budget. Thank you.