T/A 340 Block

Hi All
What can anyone tell me about a T/A 340 engine? I have heard they are more rare and therefore more valuable. My car is a 69 but has a 1970 date stamped block on the rebuilt motor. I got in touch with the guy who rebuilt it in the 80's (it has less that 5000 mi on the rebuild) and he told me he used a T/A 340 and re-built it.
I'm leving town for a few days so I will respond on my return.
Thanks for the info in advance, you guys have all been great and generous with info, I only hope I can return the favor as I gain more experience.
Darius