Project Habakkuk as a floating North Atlantic airbase

Could very large Habakkuk-style carriers have been built if infrastructure and manpower were available?

Possibly, if the concept and supporting infrastructure had been developed before the war.

Prewar development could make construction of Project Habakkuk more plausible. That prospect depends on having both the concept and supporting infrastructure ready before the Second World War. A floating iceberg in the North Atlantic would be a useful asset under those conditions. Engineering and economic feasibility remain outside this brief assessment.