Hi Scotty I have a Holley 4 barrel carb. I noticed that it never opens the secondaries. I did the paper clip trick. I also manually move the linkage to make sure it isn't stuck. It is a vacuum secondary type. Can I btpass the vacuum and put a screw in the linkage to make it mechanical?

yes, if you want to try that, just make sure it doesn't ever stick open and kill you. Me, I'd throw it away and put on a brand new edelbrock, they are tons better anyway

If I do decide to buy an edelbrock, how do I know for sure which one will fit my 391 engine (Ford 350- 1976).