nylon tubing is fine.  You'll have a tough time finding the adapter to go from a 1/8" compresion male thread to a -3 female.  just use the nylon.  its good stuff

in my mustang i used brake line hose 3-.  i figured if it coudl withstand brake pressure and fluid it would do fine with some oil. 

http://www.jegs.com/i/Russell/799/632530/10002/-1

Stand up to the pressure, yes, but brake fluid is completely different than oil. It's organic, for one, and things grow in the stuff, the rubber is a different material all together. Even braided stainless is still rubber hose inside and will fail, and weather check, etc, just the same as rubber eventually. Nylon is one of the best choices, but there is another.

I would run solid S/S tubing, Brad (1/8" if I remember right) and use the same compression fittings used on the nylon crap. Good enough for heavy duty farm/construction equipment, can't imagine a boat having more vibration, flex or abuse than that! In showing people and using for last minute projects here my pop's old JD310 Backhoe that he and I completely tore apart and rebuilt 12 years ago, (it burned up in a barn fire....no not mine, we bought it dirt cheap at auction in that condition) we had picked up a 20' roll of the stuff from the Local John Deere dealer in Niles Ohio.

We used it for not only the oil pressure gauge, but added in a hydraulic pressure gauge with it as well, since we rebuilt the radial piston hydraulic pump ourselves and this was our only way to know if the damn thing was working even close to right. I did, however, use flare fittings and a flaring tool on the hydraulic lines.........Was using the hoe just today, and the pump, and tubing is still holding up to 4500PSI spikes with no leaks! 

Ray

Brad, I ran 1/8 in. copper tubing in my boat and had great luck for years. And its very reasonable, Yo can get a 50ft spool of it at Grainger for $35 that will give you 2 runs from the back to the front of the boat. Also I have a used autometer liquid filled pro-comp 2 5/8 mechanical if you can use it, let me know.

I will be calling my AN supplier (Sweet Performance) for the parts.

There you go,, Dave will take care of you!