Robert,
Your drum/drum car probably didn't have a metering valve.
Check this Wilwood proportioning valve, it has metered valving for drums.........if you plan on staying with the drums this would be a cleaner installation than using the GM metering valve which is over $100.
http://www.wilwood.com/MasterCylinde...emno=260-11322
Here is a GM metering valve:
http://www.classicindustries.com/camaro/parts/pv68.html