I like the idea of a spread bore vac. secondary Holley. My reason,
Had one on a pontiac 69 400cu. in. and it worked real good.
Less moving parts in the Holley.
It would be new.
Less chance for something that might go wrong with a refurbished carb.
Better "feel" as to where the secondary's are in the peddle travel because of the additional spring pressure on the secondary butter fly's. You can feel right where the primary's end and where the secondary's start. It's like there's a second spring on the secondary's and it let's you stop before you get beyond the primary's.
This is just my opinion and I don't want to get into a debate with anyone and start name calling. If you want to reply with your opinion on another carb, please do.