mark50 - this conversion is similar between the 235, 261 and GMC inlines. The only thing I am aware of that might influence how you do it is that the Chevrolet motors seem to have more ribs cast in that location making the area for drilling / tapping a little more crowded.
When you select fittings - get thin wall so that your oil flow is constricted as little as possible.
Here is a photo of mine done on a 270 when complete.
This looks like a good photo step by step on a 261:
http://www.speedprint.com/deves50/oilfilterinstall.php
