Newbie AF Texan Owner - Missing Part

I recently purchased a preowned AF Texan and the prior owner failed to mention he lost the set screw for the air tank. 

1) does anyone know where to get the part and/or the part #? 

2) If it's a common set screw, does anyone know size, length, etc of the set screw?

3) (likely dumb question) is it safe to shoot without the set screw? I assume if they have one factory, its necessary for safety, etc.

Thanks for your input, wisdom, etc.