39A front sight base/ramp

Does anyone know if the front sight ramp, from the "old" style vs the "new" style, are interchangeable?
I tried removing my front post, to install a globe front sight. It won't move at all! Not wanting to damage the original (late 50's vintage) parts, I thought that I'd just put on a new ramp and globe sight.
The angle/slope of the two are visually different, but I don't know about the screw hole spacing.

Thanks!

EDIT:
1960 (T) serial number.