Can you run a np241c transfer case usde down?

I dont see why not but....

The vent would have to be relocated and the transfer case would have to be removed to drain or fill as these holes would be upside down.

No. The NP 241c has an internal oil pump which is driven by the mainshaft. The pickup is located near the bottom of the case, directly underneath the front output shaft. Flipping it upside down would cause the pump to starve for oil, and the case would fail.

However, the 241c was available in both right hand and left hand drop from the factory. Right hand front output versions were in GM trucks with solid front axles through 1988 or so. The left hand front output was common in GM trucks with independent front suspension from 1987 through 1995, and available (but rare) from 1996-2000 or so.

Be aware that there are two different input shaft spline counts (27 and 32). The 27 spline was found in half ton trucks and some 3/4 tons, while the 32 spline will be in most 3/4 tons and all 1 tons.