I have allot of experience with Mopar, "Six packs" and in Chevy speak, "Tri-Powers" Both of which are Holley setups. They are not hard to tune, if they haven't been buggered up over the years: Examples:
1. Throttle shafts worn VERY common prob
2. Metering plates and jetting. Over the years people tend to mess with these while really not knowing what they were doing
3. Changing over from vacuum operated secondaries to mechanical
4. Plain worn out carbs over the years
5. Buggered up throttle linkage between the carbs
6. Improper idle solenoid adjustment/inoperative soleniod
Most perceived tuning issues are one or a combo of the above issues. Also, when one or all carbs are removed, the throttle linkage between each must be adjusted as per manual specs. Its not a remove and then just place back on. Again, not hard but a little time consuming
Even the new replacement Holley carbs do not have the proper metering plates. Yes, they will run out of the box but are not the correct metering plates as originally used back in the day
Numbers matching will bring bigger bucks no doubt: If they arent, yes, they are worth less, but will most likely cost the new owner allot of money to get the carbs restored/in proper running condition