The main diaphragm can be replaced by one from a Series Land Rover, the diameter & holes are in exactly the right place!. You need to drill off the riveted bit in the middle though of the Rover one. The other diapragm is a compensatory diaphragm & if it goes won't leak into sump.
As it was designed for wading, if there was leakage it had to drain there rather to the ground, althogh I have heard of people drilling a drain hole to the air.
I agree with Chris I seen no point in pratting around with electric pumps, just run the thing as nature intended. Although the only exception to that principle would be to fit electronic ignition. (Better spark, no points to adjust, no synchronisation to set up/worry about, no condenser problems, giving better performance & really clean plugs)