Here is my concern and the reason I asked about the engine. If it is a flat tappet hydraulic lifter motor it needs to have the cam broken in the right way. The right way is not to start it and let it idle, you need to run it at 2000 rpms or so for at least 20 minutes and add some zinc additive to the oil or you run the risk of wiping out a cam lobe. Even with those measures lots of cams still get wiped.

That squealing might not be a simple vacuum leak, but something mechanical inside from not breaking it in the right way. I'll also bet it was never prelubed before start up.

Don