Sadly fellas, if only it were that simple, but the inlet port on 16v heads are further apart than the 8v that commonly donates the carbs, so the carb bodies are closer together than the throttle bodies basicly, so a plate on top of the throttle bodies just wouldn't line up,
a few folk have married the lower half of the throttle bodies, cut just above the coolant spout, to the top half of the carb manifolds, but it takes a lot of welding and an awful lot of blending i should think, but entirely possible,
on the plus side, this method allows you to run them up to a good height, easily as tall as the throttle bodies which are quite a bit taller than the carb manifolds, and as i mentioned before, this height (length) of inlet tract is theoreticlly better for the 16v motor.
on other notes, Mikuni Flatslides are a great carb eh Keith, can't fault the application either mate.
as for getting your money back via ebay, depends how long ago you bought them and can you return them intact and apparently un-used i should think too? and then still not quite straight forward,
its much easier to be a rogue on ebay than it is to try to be right with folk these days, it seems to be full of undesireables at the moment!!!