Prepare to measure crankcase volumes

Yesterday I drilled a hole in the top of 2 old pistons and taped up the reed valves.
Then I assembled the crankshaft into the crankcases and bolted on the reed blocks.
Now I am ready to pour some automatic transmission fluid into the crankcase through the hole in the piston with the piston at Top Dead Centre. Note that the crankcase volume is to include the volume of the transfer ports which cannot be done with the piston at Bottom Dead Centre. So I will have to subtract approx. 125cc from each of my 2 volume measurements.

I want to work out if the porting I did on the top left crankcase has made any real difference to the  crankcase volume. I am thinking that I will need to fill in the crankcase a bit to get the 2 volumes the same.
As you can see in the photo below; the LH side reed block wall is not the same as the others. I am thinking that I can fill the crankcase volume here to make it match up with the rest.