Recheck the BCC.

That BCC comes back as a 1227747 ECM, which does not control the transmission shifting. It will however control the TCC, as long as a correct VSS is connected.

Posting pictures of the ECM, with the MEMCAL/PROM cover removed will help identify it as well.

Is it possible that it's a 4L60, which is just a later non electronic version of the 700R4? Maybe the seller was trying to make it sound like something more or newer than it really is.

A 4L60E will have a rather large electrical connector on the passenger side of the case with the connector point up. A 700R4/4L60 will have a small 4 pin connector on the driver side about mid way along the length of the case also pointing up.