The current thought is to install a modified Mazda RX7 cooler in the front of my GT style conversion.
I bought a cooler off Ebay, for 10 bucks and it showed up on my doorstep today. I must say I'm quite impressed with the quality of the part. It's welded aluminum and the craftsmanship appears to be on par with German Behr parts.
I shot a bunch of pictures and thought they might be of interest to some on the list.
Here's an overall view:

The business end:

the thickness

The height:

There is a built-in pressure relief valve that unscrews (It's out in these pictures). The inlet and outlet are pretty small, and I will replace the bungs to use the 30mm fittings that are used in the oil lines to the cooler.
So what needs to be done is the following: 1) plug the hole between the two chambers at the business end, to disable the pressure relief system. 2) plug the holes facing towards the top and the bottom (they won't be used). 3) replace the bung facing the end on the inlet side with a 30 mm fitting and 4) add a complete new 30 mm bung on the outlet side, facing the end.
And do all of that without any risk of contamination to the inside of the radiator.
I'll keep this thread alive as this sub-project is undertaken.
Cheers.

That's what I have in my car. The motor is a 1983 911SC stock 3.0. The size of this radiator is right to match up with the 5 holes in the front of the 914. I didn't do all those things you are doing. Maybe I need to? The one I bought had the factory lines and I had fittings put on my oil lines to match and hooked it up. Going from the big 911 lines down to the small mazda lines causes some noises when running , but the car hasn't run hot yet at the track.

Grady

I've now seen 3 different variations of that cooler. Mine has the exits out the side. That bottom hole is plugged.

I took some threaded aluminum rod and welded them to an aluminum plate which I welded across the top attached to both ends. The rods go through the holes in the factory GT shroud. Looks like a factory cooler.

QUOTE

I've now seen 3 different variations of that cooler. Mine has the exits out the side. That bottom hole is plugged. I took some threaded aluminum rod and welded them to an aluminum plate which I welded across the top attached to both ends. The rods go through the holes in the factory GT shroud. Looks like a factory cooler.

This is due to the different generations of RX-7 (1979-1985,1986-1992, 1993-1995). Early oil coolers have inlet and outlet facing the same direction, not one in the side and one on the bottom. Despite the different locations, I don't think it adversely effects oil flow.
I think the mazda oil cooler is a very well designed cooler, because the rotary engine rejects about 1/3 of it's heat via the oil cooler, so the unit must be robust.

-Rob

In the process of transforming the cooler, I cut off part of the end where the pressure relief valve was. Here's what the inside looks like. I will obviously need to completely clean everything before closing it back up.

Not absolutely sure how this is going to work out, but this is what the modified Mazda cooler now looks like. I took it to a machine shop to have a new "end" welded together. This is how it came out:

another view

The fitting (I'll use two of them) is threaded 30mm x 1.5. I'm lucky the machine shop had a tap and was able to thread the inside of the rings that are welded to the cooler.
Here's an overall view of the cooler now.

What remains is to pressure test it, take it to a radiator shop for cleaning, and decide if I want to use it. On the plus side: once finished, it would have the general "look" of a GT cooler, being aluminum and the right architecture, and there's no reason to believe it's contaminated. On the downside, it is a little banged up and there is no way to guarantee that it is clean inside.
I must say, this part has not turned out quite as nice as I would have preferred. Perhaps others will learn from my experiments.

ive also heard that some of the rx7 coolers had a thermostat built in...


someone also made one of these that had a removable end cap (instead of welding the new end on..)

I think I remember seeing a picture of the removable end cap, but it resulted in a significant flange outside of the cooler, which would have made intallation inside the stock shroud problematic.