content: The budget friendly way of doing at least some of this is installing aftermarket HVAC and a stereo.  On my 55 Chevy I have a HVAC system made by a company called Vintage Air that only minimally impacts the interior aesthetics.  There are also companies that make stereos that look identical to the factory original but are actually a modern unit with iPod/MP3 and Bluetooth.  It's also quite common to instal power windows and locks as well.  Some power window kits retain the factory window cranks locations but simply just move the window up and down when you pull up or down.