I don't know if any regular type of metering block will work. But the kit Holley sells is part # 34-13. A power valve is not used in the secondaries.
Primary power valve should have a LOWER number than the vacuum reading warmed up IN GEAR. Depending who you ask, it can be anywhere from 1.5 #'s less to splitting the difference between in-gear vacuum reading and neutral vacuum reading.
It may idle better in gear if you add 1/4 - 1/2 turn more on the mixture screws from the best neutral setting.
http://www.summitracing.com/parts/HLY-34-13/
(Post edited due to mis-wording.) ;)