On the 3.1 block, where the oil filter screws in is an extra 'thingy' that puts the oil sending unit into a different position. Now, without this 'thingy' the sending unit could be put into the same position as the 2.8 and wouldn't need an adapter. Can this 'thingy' be removed. It doesn't have a bolt but just the opposite.....if I put a bolt in backwards it'll fit into the hex hole that looks as though it is what is holding it in. Anyone know what I am talking about?

The oil filter adapters are differant on many of the GM engines, depending on the model of car the engine is from. Yes, remove the one off the doner block and replace it with the one off the Fiero block. It does unthread.