Well...what did I find??? My replacement engine, is just that. A factory refurbished 3.6L WITH an upgraded (non removable) IMSB. That is what the AT means in the number. This is much more sturdier than the single or double row IMBS that came on early 996s. Unfortunately, I have no idea how many miles are on this engine. BUT..I shouldn't have any issues in the foreseeable future.