I've found some info on some other websites that may help you.
First, what should the "stamped block serial numbers" be for a 250 cu in U.S. block?
You didn't mention "block casting number" in your above request and I believe that is the number you need to know if you are going to find the correct block for your rebuild.
This vendor's website shows four engine differences for the 250 engine and four groups of block casting numbers for the different engines.
Go down the 2nd column until you find the 250 cu in engines.
The 4th column over has the block casting numbers.
If your present 250 block casting number matches one of those in the groups perhaps your search is over.
http://www.butlers-a1.com/chevym.htm I'm not sure whether you are saying that your engine code number now is F1210FA or if you are using this as an example.
I could not find the"FA" suffix used in a 250 cu in example.
Doesn't mean anything except I didn't find it in my searching.
Anyway, the last two letters in the engine code are the suffix of the engine code and do not refer to where the engine or transmission was built.
The "T" in "TA", "TC" or "TD" does not refer to Tonawanda.
The suffix letters refer to the engine size/transmission that was originally mated together and the year, I believe, in which that occurred.
This vendor's site has numerous examples of the 1967-68 Chevy truck suffixes.
http://www.gmcpauls.com/67-72_chevy.htm If you are interested in identifying your transmission and where it was assembled, I believe you need to find the transmission application code on the transmission ID plate. Location of the ID plate is indicated on the below website.
The "W", "K", and "S" that you listed will be part of the application code on the ID plate that is on your transmission if indeed you have a 3 speed manual built at one of those sites.
Below is a Chevy Nova site but the info on transmissions translates to all chevy's according to the website author.
http://www.novaresource.org/trans.htm Happy ID hunting.
I hope this info gets you a little further down the road of completing your project.
