There's not really much in the line of choices, one thing you'll need to know is what flywheel you have. If the 12 volt conversion used the original 6 volt starter (not uncommon) then you will have the early "wide tooth" flywheel, the later flywheels have a different tooth patter/count and while interchangeable, only work with they're respective starters. So, what you'll need is either a starter from a passenger car 6 or Hydro-Matic equipped truck. These are the only ones that will bolt up to you're bellhousing, but they will convert it to a key switch start. Oh, and you'll need an ignition switch from a key start vehicle, too.
One question, are there any other reasons you want to do away with the foot starter other than the reasons you list? Those starter are really easy to overhaul, and are more reliable that what they put on cars these days (I know, I replace alot of them, including 4 on my own late model Blazer). i everhauled the one in my '55 for about $12 (parts and electrical cleaner), and it starts up every time.
