Shane,
Back in the dark ages,1970 and 1971, I was a mechanic at a Buick Dealership. My shop manual tells me that a three speed transmission with a column shift was an option. Hurst floor shift kits were the cool thing to do in those days and were readily available for about anything with gears.
I would not recommend a switch, it sounds like you have a solid vehicle in original condition. I don't think any performance gain will be worth the work and down time.
