Commission a survey
. An original A4 in seawater since '63 is maybe not so good...unless
it has a freshwater circuit. But a rebuilt one from, say, since 2000 is probably fine.
A survey will reveal major defects if any. Expect rot
in the stringers, etc. It really depends on how well they've kept the boat up for sailing purposes. Liveaboards tend, in my experience, not to, i.e. worn halyards, seized winches and sheaves, cracked blocks, etc. This is not always the case, but some boats never move and their ability to do so is reflected in the state of the rigging