Hey signdude, welcome!
As the others said, that's your frame's basic part number.
In case you were not aware, Ford's numbering system (engineering numbers I think they would be called?) run down like this:
The "C" is for the 1960's
The "6" is for the year, so 1966
The "T" is for Truck line
The "A" is for the first Revision
The "53051" is probably for basic ladder frame category, but others can clarify
The "2A" is probably another level of revisions, but not sure.
In general, you'll find "T" parts on Broncos when they are unique to trucks (or Broncos alone) and other letters when the part is shared by other automotive lineups. Such as a 289 V8 that might be listed under the Falcon line.
A part number like yours "might" have been used over multiple years however, so it does not always indicate a specific year. The actual VIN or other determining factors can narrow it down sometimes though.
If yours is an early '66 with the forward canted rear shock mounts, that "C6TA" may be unique to one year only Broncos.
If it's the later style with the rearward canted rear shock mounts however, it's possible that same frame number may have been used for a couple of years. Any time a change is made that's large enough you get a new part number.
My '68 then might have a "C6" or it might have a "C7" or even a "C8" depending on what changes, if any, were made.
Don't know if you knew any of that already, but figured I'd throw it out there in case it helps you down the road.
Good luck. And definitely post up some pics!
You can become a contributor for 12 bucks a year and upload images directly to your discussions, or you can use your "garage" feature to upload some that we can see if we click on your link. Or if you use an online image hosting site like SuperMotors you can upload your pics to that site, then link them here.
Definitely give it a try.
Paul