I have two tanks with gauges and the tank that I won't be using appears to have a much nicer gauge assembly inside, so I would like to swap the complete assemblies.
There are two specialty tools (that are available from vendors) that are used during this task. Might I suggest you consider ordering a new float when you purchase the tools as many older cork floats are deteriorated after that many years. There are even new floats available for use with ethenol fuels.
Check the archives, there has been plenty of discussion on this. If you are ordering the rebuild kit, make sure you get the one with cork gaskets, the neoprene ones seem to always deform and leak after I tighten them up.