There are a few more differences than that; the TL-51 is the only kit pre-drilled for a string-through-body bridge (though from the picture on the PBG site they are drilled rather badly and don't line up at the back) although no string ferrules are clearly shown in the kit photos (the top photo seems to show ferrules or maybe press-fit bushes for the tuners, but the detailed kit pack picture shows screw-in bushes for the standard TL pack tuners so I'm not sure what you get). Note that all the other TLs come with a top-loading bridge.

Although it comes with Kluson tuners; as the PBG site mentions, you'll need to order special adapter bushings so that they don't rattle around (so add a few more $ to the overall cost).

It comes with an 'ashtray' bridge cover, but a huge one that looks more suited to a Fender bass than the one that was fitted on a Tele (probably because it doesn't come with a proper old Tele style bridge with upturned sides that the cover clipped on to).

Also, the kit comes with a standard TL scratchplate, which means that the bridge pickup and mounting hardware is designed for scratchplate mounting, unlike the early Teles, which all had body-mounted bridge pickups.

Simple things, like the neck plate with a rubber/soft plastic backing are certainly not very 1951.

Also the top picture shows a square mounting plate for the output jack (like many Gibsons) and not at all like a real (or almost all the copy) Tele.

So overall it's slightly more Fender Tele like- but not that much - and hardware wise it's really not like a '51 Tele at all.

If you don't plan to bother upgrading much from the standard kit hardware and aren't bothered about a really vintage looking guitar, then like Waz I'd suggest the TLA-1 or TLA-1R (depending if you like a maple or rosewood board) but go for the Grover chrome 205C mini-Rotomatic (standard or locking at your discretion) upgrade option for the tuners. If you really want a string-through bridge, then I'd suggest getting a Wilkinson unit plus some rear-body ferrules and drilling the holes yourself. As long as you have a pillar drill or drill stand, the holes are easy to drill. I've only done it once (plus one practice on some scrap wood) and got the rear holes in a very neat line (which must mean the Chinese factory workers are doing it by hand on the '51).