I think he was probably just misunderstanding your writing of "many years ago" and "It was loooong ago" as meaning longer than 10 years, which is understandable.
Anyway, back on topic. I've only tried them in shops, but the 604 has technically nicer finishes, but biggest difference is the controls. The 304 has the presets, which are actually pretty cool, but again this is only from briefly playing. The 604 had a fill 3 band so was a bit more control and can really dial in your tone if you want. Both feel pretty similar, maybe the 604 had a slightly nicer neck. You'd probably be pretty happy with either if you like the look and shape, but electronics are different so need to consider that.