Oil and water line fab?
 

Okay so I was in Advanced yesterday and this is the first time I noticed that they sell multiple sized hardlines like the ones under our cars for fuel and attached to the firewall for clutch/brake fluid. I'm wondering if anyone has ever considered or attempted using these to make an oil feed line and possible a drain line. They may be too small for drain lines, but the idea came to mind and it reminded me of FM's hardlines. Any thoughts on this?

Ive seen (not on a miata) where they used brake line as an oil feed. Looks nice but id be worried about metal fatique.

Those are steel lines intended for brake line/fuel line use and are excellent for other purposes as well. Rated for LOTS of PSI. Steel does not fatigue like aluminum, but it can break if overstressed. Observe how the OEM brake/clutch hard lines are secured at their ends where they transition to flex lines for examples of how to avoid breakage issues.

Since they are steel would I have an issue with rust inside the ones running water/coolant? Also, the guy who I bought the majority of my turbo parts from gave me a stainless braided oil feed line and on both sides there are unknown male fittings instead of the usual female fittings on oil feed lines. The one side has a 90 degree turn and the male fitting looks to be the same as the one on the brake lines and it moves freely over the solid part like the brake line fittings as well. Has anyone had any experience with an oil line like this?

I've only experience with stainless braided like most here use, but as we've discussed before: the brake lines/steel lines should work fine if you support them properly with brackets and don't bend em too much.

I intend to take this route on my current setup as well. If it doesn't work I have stainless braided line to replace with. Should work though since most OEM's use this method
Keep us posed if you try it.

Your block is made from cast iron, so as long as you run enough coolant in your water to prevent that from rusting I wouldnt worry about some steel lines.

Have you figured out how you are goinIg to go from the headlines to the turbo/block fittings? To use the 3/8 -24 on the hardline it seems like you would have to use a series of different fittings to end up at the correct fitting for the block/turbo which is way too many failure points. I've found this Russell Hard-Line AN Tube Fitting Adapters - JEGS and im thinking this is going to be the way to go. Any thoughts?