The serial # on my '63 T-20 is 1857, thats around 200 units away and may be from the same year.
Going from memory here because I'm too lazy to look it up. T-20 would be a '62 or '63. I don't recall seeing any '61 T-20s and they grew a foot in 1964
to become the t-21.
was the first year they used anodized aluminum for the skin. Prior to that, they used raw aluminum panels you can polish. Admittedly, after 48 years, the two look identical but you might be able to make a shiny spot on the '62 with a pencil eraser. The '63 will simply laugh at you for trying such a silly thing and may go a shade darker just for spite.
That said, its turned out to be a fantastic, classy and durable little trailer.