I didn't know if I needed to remove a fan to see it. Or if so, which side?...
Either Fan will give you visable access to the thermostat, in order to discern a leak. If a leak is present, then you'll have to access the Screw Head on the hose clamp (to the Y-hose)... If you're lucky, then you can access it from whatever side (fan) you just removed, otherwise you'll have to remove the other fan as well.
Hint: The right side fan is easier to remove than left side.
Hint: When reinstalling fan, Ok to leave out the upper-rear-most screw... it's not needed, and makes future removal/installation easier; also helps to replace the remaining screw/s with (SHCS)Socket Head Cap Screws, which can very/more easily be turned with an ball-end allen head wrench.
...If that is not the cause of my leak, are all of the smaller coolant and vacuum lines accessible from the sides where the fans are removed? Should I drain the coolant and remove the radiators regardless to get them out of the way?...
No, some of the coolant lines are beneath the carb, requiring removal of the carb. That said, the typical leaks are from the joints to the Thermostat and radiators, due to presence of "clear tape" on the mating surfaces for the hoses.
No, most all the vacuum lines are beneath the carb, and under the left intake manifold. You won't see any more/less of them by removing the fan/s
No need to remove the radiator for this first step of Finding the Leak... With one or both fans removed, you will have very good visual on many coolent hoses.