From the Delco regulators that I have, the six volt ones have a long cover screw diagonally placed in two of the corners of the case. The twelve volt ones have a lower flange at each end on the cover with a short screw in the middle at each end.

1951 GMC 1 Ton Flatbed -- It is finally on the road and what a great time I have driving it!
1951 1 Ton Completed

My Chevy Master 4 Door is on the Road!