Mechanical gauges don't have "senders" really. The water temp one has a "sender" of sorts that is connected to a copper tube (surrounded by plastic or rubber) that fits into the lower intake manifold (no isolator necessary, or even possible). You may need (I did) a different adapter for the lower intake if you still have the stock one.
The oil pressure has a plastic line that runs from where ever you mount it, to the engine bay. There is a SLIGHT possibility (only if you really kink it, nick it, or it's really really old) that it will leak. The isolator keeps the oil inside the engine bay.
All of the autometer models really differ by their color and lighting really. I got the Ultra-lite 2's. I like 'em. I should have gone with C2's though, because they would have matched my car better.
Any more questions? I did this all about 2 months ago.