I have read that you can drill the manifold or drill the exhaust down pipe to install the pyro probe for the egt gauge. Is one better than the other?

 

To get an accurate reading it should be in the exhaust manifold and about an inch from the exhaust port in the hottest cylinder. In the two valve engines this was the front cylinder on the drivers side, I would think the same configuration would hold true for the three valve. The manifold is easy to drill and tap. use some heavy grease on the tools to keep filings from getting in the manifold and getting to the converter.