How cold is it when you have trouble starting the engine? The 2GMs do not have glow plugs. My 2GM20F has trouble below 50*f, which is about 10*c. To start the engine the throttle should be full open, (keep a hand on the throttle) as soon as the engine fires close down the throttle. You want the RPMs to be around 1000 to 1200. There will be a lot of black smoke and the engine will sputter and make some noise at first but it will clear quickly.
I would not use ether to start a diesel, If anything I would use WD40. Good luck and let me know how it works out for you.
Or the problem comes from being upside-down.