GT-6/Spitfire brakes

[MJSUKEY@cs.com]

Getting ready to do a rear brake job on my 73 GT-6.  Sometime in it's past 
life the larger MK3 drums have been replaced with spitfire components.  
Purchasing shoes should not be a problem since it appears that the same shoes 
were used throughout the spitfire lifecycle, However I want to buy new wheel 
cylinders and it looks as though 3 different P/N's were used depending on the 
year.  Any suggestions as to how I can determine what wheel cylinders I need 
to get?

Thanks,
Marty S.