I know this is probably an unpopular opinion these days but as someone that drove front drum brake cars in my youth and the owner of a 68 convertible 350 auto front drum cruiser now I would suggest that by your description of your driving expectations and since you just bought this car to try it out first and see if it fits your driving style, you just might save yourself a lot of time and money. When I was a younger more aggressive driver I needed and expected much more from my engine handling and brakes in my firebirds then I do now. My expectations now are to have a nice top down cruiser that runs cool and on pump gas and is mechanically solid and works as it should. The only caveat is if you have manual and not power drums. if you don't have power I would add it as you will need it anyways if you go disc in the future. If in good mechanical condition drum brakes work just fine in a casual cruiser. I know to younger people that did not drive front drum cars back in the day this probably sounds unbelievable but you have nothing to lose and can just ad disc in the next off season if they don't fit your driving style.