show us the rest of the transmission. Could be a 350C, they had a connector for the lockup wiring. THis is a 350c case, looks close, eh?
^this @squirrel nailed it. I almost bought one as a th350 core and passed. They can be converted to non lock up with enough parts swapping - if you already own it.
I remember that there was a transmission that looked a lot like a 350 but there was a band adjustment thing on top of the case.
I think these came out in '81 to replace the existing th350's. Buick and GM huddled on it, and it only lasted a few years.
Yes they is the Th350C with lock up converter. Electronically you could lock up converter and drop 250 rpm or a bit more. there are lockup kits out there or you could run manual toggle switch and energize at cruise speed, then shut off at times trans is shifting. Or just say screw-it and just install and run as is and won’t hurt a thing. Running one like that for years.