Have a look at this report: NASA Breakthrough Propulsion Physics Program https://ntrs.nasa.gov/citations/19980201240 Published 1998
This stuff was all quite open at the time. In the UK, British Aerospace was also funding antigravity studies, in the shape of "Project Greenglow" - which was mainly Dr Ron Evans, who was based at their Warton aircraft plant, in Lancashire. At around that time I went along to a talk Ron gave, organised by the Royal Aeronautical Society, at Warton. He described various aspects of his own project, as well as the Evgeny Podkletnov work, and the NASA program. This was all activity that you could imagine would be described as "top secret", if it cropped up in some fiction novel. However, the researchers seemed to be approaching it as a totally non-classified and open area of study. For Ron Evans, it was just the continuation of a hobby interest, prior to retirement. And, as far as I can remember, the actual budgets were tiny.
