High Pressure Steam- Tapping a Blind Flange- Urgent Advice

I was hoping that someone else would jump in on this before now and offer something. It did not happen, so, I will try.
You say you have a space problem. Okay. how much of a space problem?
From the face of the fixed flange, how far is it to the obstruction?
What is the orientation of this problem? Is this like a drip leg that will draw off liquid from a gas stream? Are your limits between the face of flange and a floor, the paving or grade?
What is your limits on obtaining other piping materials?
With-in the time frame of the project can you obtain a 16" x 8" reducing Weld Neck Flange and an 8" Short Radius ELL?
I am suggestion a Reducing Weld-Neck (instead of a modified Blind flange as a Slip-On) then a Short Radius ELL (instead of a Long Radius Ell).
Another point. None of the Slip-On Flange charts I have show 600# Flange/ELL combination dimensions. So assuming that you insert the ELL 3/4" into the 3" thick Blind Flange 1-1/4".
The difference between what you have planned (as best as I can tell) and what I am suggesting is 1-1/2 inches.
You also did not define any Insulation, so both methods must allow for the some thickness for the insulation,

Something to think about.