I just ordered this from a friend. Should solve the v6 mounting problem.
Low Profile 92mm to 80mm Fan Adapter by beley45
An adaptor to convert a 92mm fan opening/mount to use a 80mm fan. All the adaptors i found on thingiverse were to thick to fit in the space i needed. This is designed to be used with the standard fan screws(the ones with the really coarse thread). They Should bite into the outer holes(92mm) but...www.thingiverse.com
Hope the pump-res is not too heavy but I guess you could support it through the fittings.
It’s got some weight to it, but I reckon that should hold it without issue