You mention you are putting 3 gauges under the dash. Is there something wrong with the water temperature gauge that is already in the speedo assembly? The mechanical gauges are prone to dying due to the fine tube breaking but they can be resurrected or transplanted with electric. I went with the latter.

http://amazoniac.wikispaces.com/Electric+engine+temperature+gauge

For oil pressure I used brass fittings into engine. Female tee with hex nipple into the block, original pressure switch screwed into the front branch of the tee and pressure gauge fitting into the back branch of the tee. I have the plastic hose but I ran some 1/4" irrigation tubing over it through to the dash to protect it from damage.