This is a new one to me. I think I recognize the box art; beware my notorious memory, but I think it originally appeared on the tiny little Airfix Golden Hind. That kit was one of the company's earliest releases, back in the early or mid-fifties. It was about three inches long, and was packed in a plastic bag. The artwork appeared on the paper "header" that was stapled to the bag. Airfix enthusiasts (at least those of the ten-year-old variety, like me) learned the hard way to take those staples out carefully; the header had to be unfolded to reveal the instruction sheet.
That old kit, though, obviously isn't what's in the MPC box. I'm inclined to agree that it's probably a repackaging of the Revell Golden Hind. (The dimensions and the reference to the crew figures are the clinchers.) I wasn't aware of any Revell kits having appeared in MPC boxes, but plastic kit molds do get around.
In its original form the Revell Golden Hind is one of my all-time favorite kits. In earlier Forum threads we've established pretty firmly that it's based on the work of a German modeler named Rolf Hoeckel, who published a number of books and sets of plans back in the forties. He, in turn, quite obviously worked from the famous Matthew Baker Manuscript in the library of Cambridge University. The Baker drawings are generally referred to as the earliest surviving plans for English ships. They're beautiful pieces of draftsmanship; they've served as the basis for just about every reconstruction of an English ship from that period - full-size or model - for the simple reason that there just isn't anything else to work from.
Just what the ships in the Baker Manuscript are is the subject of considerable discussion among experts. The manuscript dates from right around the time of the Spanish Armada; Baker himself apparently was a master shipwright in Elizabeth I's navy. The general assumption is that the drawings depict several up-to-date English galleons of the sort that sailed against the Armada, but nobody's quite sure.
At any rate, those tall structures on the bow and stern of the Revell Golden Hind are entirely consistent with the Baker drawings and virtually every other contemporary source. In fact they're a little less "swoopy" (I like that term; it really fits) than those of the big ships in most of the Baker drawings. Futhermore, it's likely (though by no means certain) that the Baker drawings represent what was referred to as "race-built" galleons - which, by the standards of the 1580s, had a considerably lower, "racier" hull form than was standard in previous generations. And the typical Spanish ship of the period almost certainly was taller for its length than a "race-built" English one.
There have been a number of efforts to reconstruct the Golden Hind since Herr Hoeckel's day. (If you do a search on "Golden Hind" here in the Forum you'll find quite a few threads that discuss the subject in some detail. Example: /forums/t/72084.aspx?PageIndex=1 . ) My personal opinion is that the Hoeckel/Revell design still holds up pretty well - in view of what meager evidence we have about the actual ship.
There is, however, just NO WAY that the Revell Golden Hind kit represents a Spanish galleon! (Revell itself reissued the kit with that name attached to it at least once; that was just one more of the company's notorious marketing stunts.) To begin with, the Golden Hind was far too small to earn the label "galleon." And the shape of the hull is distinctively English. The Golden Hind was no more a Spanish galleon than H.M.S. Cossack was a Japanese battleship. (It's worth noting that the label on the box doesn't include the word "Spanish." Presumably somebody in MPC's marketing department, though he/she apparently didn't know - or care - what the word "galleon" meant, did notice the English flags and the English royal arms on the sails in the box art.)
I guess it would be possible to use this kit as a basis for a major conversion. I'd recommend starting out by changing the scale; if those crew figures are in scale with the ship, it's too small to be a galleon (Spanish or otherwise). Unfortunately we know even less about the appearance of Spanish ships from that period than we do about English ones. (There are some contemporary Spanish treatises on shipbuilding, but they don't include any drawings that are comparable to the ones in the Baker manuscript.) In all honesty I've never seen a model of a Spanish galleon that really convinced me - but the big old Imai kit is the most believable reconstruction I've bumped into. Would that the kit were easier to find!
The flip side of that coin, of course, is that, since so little is known about the real things, nobody can say for certain that a model is "wrong." If one keeps that point in mind, and does some reading (I recommend starting with the Conway book I mentioned earlier: Cogs, Caravels and Galleons) , such a project could be really instructive - and great fun.
Good luck.