D2 oil cooler tube threads

I found those threads to be UNF as in the same as a fine thread bolt of the appropriate size.
I went through the same thing as you are and the local hydraulic and fitting supply stores couldn't supply or identify the fitting.
Found a , I think NPT fitting that was slightly larger and ran a UNF tapping die down the thread and this worked fine.
Only got stupid answers from the blokes at the hydraulic stores.

In an old thread OM identified what it was?
(4 or 5 years ago)
This one! "Get a couple of dash10 Oring Face Seal plugs from your local hydraulics store. Slip a #116 oring up to the shoulder, add your preferred thread sealer and forget about the oil cooler."
http://www.acmoc.org/bb/showthread.php?24069-Question-D4-7U-Oil-Cooler
This will/should get you close to a proper fitting.
One other thread was mentioned to take the fittings you currently have and tap them to 3/8 npt. (he plugged them for a bypass) In your case you should then be able to use 3/8" hydraulic hose on standard fitting.
I believe it was Lance in AU that said it is actually a straight fine bolt thread.
One other fellow suggested leaving the pipes going to the front (old J series) and making 2 small manifold adapter blocks, then brazing a piece of tubing between them. This would allow oil flow from the top port to the bottom port. With the Chaff Guard installed, no one would ever see!
I remember reusing the fittings and using new stainless steel tubing to create the bypass loop on a J series.

Thanks guys this helps a lot.

Neil - did the epoxy job work to seal your oil cooler?

Cheers

Well, now that I've dug the tubes out to see what size they are, I might as well clean them up and install them, then set up a big pan underneath! : ) Have to remove the radiator in the next couple of days so I'll hook it up after that