Update!
I think I solved what I wanted to do. I bought this to install in the back of the block and then run a line to the factory gauge:
http://www.speedwaymotors.com/Straig...o-AN4,954.html
I may run a "Y" fitting on this to feed the aftermarket gauge as well or just buy a 90* fitting and plumb the aftermarket gauge from the port above the oil filter.
This should take care of the issues in hooking up AN lines to the stock gauge:
http://www.speedwaymotors.com/Gauge-Fittings,949.html