I can't see how fuel can get into the sump via any other way other than the pump.
A failed diaphragm is the most common way for fuel to get into the sump, but a flooding carb will drain fuel into the manifold, which will enter the engine through any open inlet valves, and drain easily past the rings to the sump.
I have been following this subject with some interest. The chances of the pump suddenly oversupplying is, as the engine ran OK before the coil was changed, practically nil. A pump may start to UNDER supply due to a number of factors, but not oversupply.
Any pump will have a designed output pressure, determined by the spring under the diaphragm. I agree, it is unlikely to increase its supply pressure with age or use, but if initially supplying excess pressure, many float valves will cope for some time before succumbing to the pressure. As the engine had not apparently been run for long since 'new', this should be considered along with any other diagnosis.
The amount a pump supplies can, to a greater or lesser degree, be adjusted by the number (i.e. total thickness) of gaskets between the pump and the spacer (or spacer and crank-case). This is the method recommended in the workshop manual as there is a set amount that the operating rod should stick out past the spacer.
The number of gaskets does not really adjust the output pressure, as that is determined by the spring pushing the diaphragm. More gaskets can reduce the input 'suck' as the diaphragm moves less, which can lead to insufficient fuel supply if the tank is a long way from the carb. With the power of even the 650 motor, this should not be an issue.
The main purpose of adjusting the number of gaskets is to reduce the stroke of the lever, and so that of the diaphragm. This will flex the diaphragm less, giving it a longer life. Decreasing the gaskets, can compensate for a worn pushrod or cam lobe.
The more likely cause of the problem is the needle-valve sticking open, possibly by a bit of grit/dirt/rust
Absolutely, this was mentioned earlier, and still is the primary thought in my mind, or a porous float.
I have a feeling that the float may indeed have had some fuel in it! When i shook it a bit yesterday it did sound as if there was something in there. Not much and it didn't drip or anything but it did feel a bit a odd. I will recheck this tomorrow.
Any fuel in the float will change its level, and lead to flooding. Any doubt, replace it.
The car does tend to be parked in a slope as i have a ramp. When i did this again tonight and went back a couple of hours later the floor was full of fuel yet again and the oil really runny so i have had a lot of contamination - more than could be justified by 3 failed attempts to start the car.
The problem showing whilst parked on a slop eliminates the pump pressure as a problem, as once the diaphragm has let go completely, the engine is not running to retension it.
Gravity alone is allowing fuel to flow, through the pump to the carb. The float and needle valve are under almost no pressure, so either the float is porous, or the valve not sealing due to dirt.
Another thought. I understand that the ethanol content in current fuels can attack some float materials, and valve seats.
I removed the carb cover again and this time I actually pulled the pin that holds the float. Lo and behold the damn thing is FULL of fuel. It had two almost invisible hairline cracks and a pinhole in the jbweld like seam that runs in the middle! Submersed the whole thing in water and there were lots of bubbles forming. In my anger I squeezed the damn thing and lots of fuel popped out of it :devil:. 
