A really good choice if you are going to leave it stock is the '61 - '63 year w/ 3x2s and a solid-lifter cam. These were rated at 401 HP (a bit overrated). Course, that won't be easy to find. You did say best 390.
THe GTAs like you had were 335 HP and not bad. Seems to me the later year engines had the screwed-up pollution hump. Have to look at the book to jog my memory on that.