Front Hat Bolts on a Enderle Birdcatcher:
On Birdcatchers …. we use a short stubby ratchet w 3/8” drive, or a bent on a 45 degree box end if you are using regular head bolts.
Usually, you can take out one butterfly at a time and easily get in there, no need to take out the shaft. The butterfly must have a .010” gap on the bottom when you are done and it is beveled in one direction.
We used to drill and tap the area right above the bolts and then tap it 9/16”-18 threads for -6 AN o ringed flush plugs.. then you can easily put a allen socket down through the holes.
Be sure to use some AN Washers on the bolts, and either a drop of Loctite, or a lock washer.