I managed to locate a couple of drawings on microfiche, which enabled me to determine the pendulum 
dimensions you want for the C40B Waiting train. 
I scan the microfiche but there is a loss in clarity when the picture is enlarged, 
so I have marked up a drawing with the dimensions you require, obtained from other 
microfiche scans.

To make sure you can read the dimension, the details for the rod that is cast into the bob are :-
 
Material 3/4" X 1/4" MS bar 18" long and 5.25" is cast into the bob. The part that goes 
into the bob need 
to be drilled with 4 holes so the casting is firmly bonded to the bar. The other dimensions 
for fitting the bar 
to the crutch can be made out on the other attached drawing.
 
The bob casting works out at 8.5" long and 5.3" diameter I think that this should be 5.25" 
diameter but if you have 
the larger, you can always turn it down. You can check the correct diameter as the weight of 
the bob should be 40.75lbs. 
I think this is complete with the bar in it. This compares with the ratios of the C40A size 
which weights 30.5lbs and has dimensions of 6.5" long by 4.25"dia.
 
I hope there is sufficient information but if you have any queries please get back to me.