how to connect this steam radiator?

During a house renovation, in a room that used to be a kitchen, I discovered a number of pipes beneath the floorboards. One of the pipes was for steam heat, so I decided to add a radiator to this room. I opened the pipe by removing the cap and added a short extension pipe as a starting point for a future radiator connection. I then finished the floors around it.

Somehow—naively—I assumed that the extension pipe would be plumb, but it turns out it’s not. Since the floors in this old building aren’t level, I’m unsure how to proceed. If I attach a valve to this crooked pipe, the angle between the pipe, the valve, and the radiator might be too steep for a proper union connection.

Should I try using a longer extension pipe and attempt to make it vertical? Or should I consider a different method for connecting the radiator?

EDIT (extra details):
1. the pipe you see under the floor IS slopped back towards the main (one of the few things i did check)
2. the steam pipe is coming from under the wall (the wall you see behind), so if i put the radiator where the yellow level is, it would be 90deg from pipe to radiator
3. i played with putting the radiator as Mad Dog suggested close to the wall on the left of the picture BUT then i would have 6in gap between radiator and the wall…

(what pipes look like under the floor - now closed):

Photos showing how out of plum the pipe is: