I kept our 59 original for 4 years. I had a dream of modernizing it mechanically but keeping the original look. Finally last year we replaced the front clip, engine and transmission. It now drives much better, stops much quicker, turns more easily and gets me 20 mpg. I DO NOT miss the old drivetrain and soon will not miss the old split bench seat. It looks stock until you open the hood.
My opinion (for what it's worth) is if you have something in as good a condition as yours it would be a hard choice to do any irreversible mods. There are lot's of ways to make it safer and more efficient without cutting any steel.
I wanted to be able to drive ours constantly and anywhere. This meant a more radical mod. In it's old condition my wife couldn't drive it. Now she loves to drive it even over her Cadillac. I can cruise on the interstate and the only people that know it's not stock are the few car guys like us. Most people just smile and wave. Looking forward to see what you do.
