Paul,   To make S-beam installation easier, how about drilling a 1/4"
hole in the flange  opposite the bolt  holes.  This will provide a
nearly straight shot with the 5mm  allen wrench.  A couple of the
holes are still at a slight angle so a ball end wrench is the way to
go.   Braze washers around the hole so  strength is not compromised.
TIG braze /silicon bronze rod.    Jerry

Not a good idea. Stick with the ball end allen's.
You can plate the whole bottom with .065 thick 4130
sheet over the width of the engine plus an inch or two on
each side and then you can drill the 1/4 inch access holes.