As someone who recently undertook a lot of welding (as a complete novice) on my car after a failed MOT, I can say that I found welding overhead was very difficult. If you have access to a lift, it might be okay. But I just had mine on 4 jack stands as high as they would go, and it was difficult!
On another point, I thought I knew where this was, but why can I see daylight through the hole?