Help with V6 Engine Suffix Codes

[JimmyS10]

Talk about frustrating! Anyone called GM recently? After an hour and a half on the phone with 6 departments I'm no further in my quest than I was earlier. Hopefully someone on this board can help.

I am in the process of building a hot rod 28 roadster. I've decided to use a GM V6 powerplant for a number of reasons. Anyway, I was able to pick up a V6 pretty cheaply. Before putting in the roadster I want to rebuild it. In order to rebuild it I have to identify it so I get the correct parts. Seems simple so far, right? Well, everyone wants the year, make, model and VIN of the donor vehicle. I tried to explain to GM that is what I am calling them for. If I had that, I wouldn't need to be calling. Anyway, the VIN would only be valid IF the engine was the original for that vehicle. So, I'm looking for info from some of you more knowledgeable folks. Here's what I have and am trying to identify:

GM V6 4.3 L 4bbl carb
Engine ID = T1121UTC
Block Cast = 10105867

I know T = Tonawanda Buffalo, NY
1121 = 11/21
It appears to be an 87-91 based on the casting number.

Can anyone help identifying this engine further? Thanks in advance.