Same recommendations as above. Some of the repop slant six manifolds already have an O2 sensor bung that's OK if you are not running a turbo. If you are using headers or a turbo, you'll need to weld in a bung, no big deal. The biggest "gotcha" is that you'll need to give it a good ground. Don't run the ground wire to the sheet metal; ideally you will want to ground it to the battery, with the block being an OK alternative. And if it has a separate control module and gauge, you must ground them to the same point.