Header/riser allen key

[wakesetterDD]

I would like to remove the header or riser (?) so I can fix the plastic screw-in water outlets; they are leaking; I can't spin them in more with the header/riser in the way.  The plastic pieces screw into the hole visible in this photo:  https://photos.app.goo.gl/zarShzrjYwZu3WBy5 

Two of four allen bolt heads on the header or riser (?) are accessible but the other two have very little 'clearance' so I can't get the allen key in properly.  Any advice?  Anyone know where to get a

5/16" allen key with a very short head (the short end)?

[tvano]

i had multiple allen wrenches of that size so i diked one off and used a box end to spin it

[Chaabo]

Exactly!

Use a grinder and cut one to fit. Then use a box wrench (ring spanner) to get enough  leverage to turn the allen key.