Aha, you may have something there Trevor. I have been looking for the type of target used for Gee-H radar bombing and that is from the late 40's into the 50's. I posted a question on Gee-H a week or so back but got no replies (not that I expected any really) and this may be the elusive Gee-H radar target. I thought they would be quite a way offshore, miles, but it could be a prototype or a proof of concept version.
Could you post a rough sketch of what your memory recalls it might help? Doesn't have to be accurate, the nearest inch will do