temp, alt, oil pressure gauge ideas

The longer the sweep of the gauge, the better the accuracy. The OP pic in #1 the water temp is barely a 45* sweep. The 90* or 270* gives better resolution. The ones in post 7 look good. I have a 225 Buick OddFire motor in a Jeepster, the only easy pipe plug for the mechanical sender is in the water pump inlet - coldest water from the radiator. The 45* sweep gauge moved so little I thought it was broken. Nope, just needed more resolution. A 90* sweep gauge was way better. Make sure the intake has enough depth for the bulb if using a mechanical gauge. I usually test on the stovetop with boiling water - should show 212 in boiling water, not hitting the bottom of the pan.

For oil, a 1/4" tee and a close nipple will usually let you have a factory sender and a gauge.