The pickguard is a DIY stick-on item; how easily it will come off after 50 years - and how much of the guitar's finish it will remove in the process - is open to conjecture. FYI, they came in a set of two (upper and lower), cost about $2 as I recall, and were originally used by flamenco players to help protect the top from the incipient stages of "Willie (as in Nelson) rash" when using
golpe and
rasgueado techniques; you'll also see some '60s Gibson "folk" models (the FJN in particular) that came from the factory with a similar setup...
My thoughts:
1] $400 is unquestionably below market value - while there may well be legitimate reasons for the low price (the primary one hopefully being that this guy really doesn't know what it's worth) ask a lot of questions, preferably off the public forum;
2] As long as it's not a total junk job and you intend to keep it for some time, it'd be worth investing another $400 or so in restoration/repairs if necessary;
3] Unless you're planning to use it in a classical setting, don't sweat the pickguard - it lends an authentic folk-era period vibe to the mix...
4] Learn how to play "Puff the Magic Dragon" ...