Thank you and many thanks for checking this!I did a little Google research and it appears there is no definitive answer there. However actual film used models are not in abundance there. Granted, I only did a quick search, I'm sure others here know more about the actual film models than me. From my search it seems they are pointed in just about every direction except up. Some are down, some are angled in, some are even angled out.
All I've ever owned were the original 1980 model and the toys for the action figures. To my recollection those were down, but we all know toys aren't always correct. So, I guess anyway you want to go with it is fine.
Regardless, that is a beautiful piece you have there. Great job!! I would kill for one that size!!