That is not a very good intake manifold, but it would not keep the engine from running. I think your mechanic is missing something else that's wrong. If you really want a different intake, then get one to fit a small block Chevy engine prior to 1987. The engine number stamped on front is not an original stamp. The characters are too large, not in line, they don't match what Chevy stamped on engines, and they are stamped "upside down". The size of the pad it is stamped on does tell us a little bit about the engine, which is that it's newer than the mid 1970s (it's a short pad, not the long one that was used on earlier engines). But that's all it tells us. If you look at pictures of other Chevy engine stamps on the internet, you will see what they are supposed to look like.
The adapter he originally had is made by Holley. The adapter and spacer is not his issue. They actually tend to work well if everything is done correctly.
I may have missed it, but what are you hot start issues? Hot start can be a timing problem too. Sounds like your engine was lean previously, did you damage pistons or rings? The original adapter you had is the Holley one and much more appropriate than the square open spacer you had. Your fuel pump sounds suspect, and it sounds like you might have a passage plugged or component failed in your carb. It sounds like the shop is chasing you the wrong way to fix the problem. I don't believe that your intake is the issue. That's a 4160-style carb, if it's the 1850 part number it's 600 cfm. There is a lot of information online about tuning Holley carbs, it sounds like you need to learn some because the shop doesn't necessarily know.
Starting with the Holley website. The manifold is a red herring. There are probably any number of screwed up things that are hard to diagnose without the engine in front of us. But the manifold is just a lump. It may not be the best, but it won't stop the engine running. BTW is this in a cobra kit car or something?
Yes agreed, I have quite a bit of learning to do and yes, it is a Cobra kit It's been on my bucket list since I first saw one as a kid, I've waited 50 years for it
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