Thanks for all the replies - appreciate the info. I have made up a pattern and it does seem like the 15kg Rocna will fit, so will try that I think.
The other interesting thing I found was that, although the Lewmar winch manual said my gypsy was a rope/chain gypsy, turns out Bavaria did a special order chain only gypsy, since they figured the anchor well is not big enough for rope and chain and wanted to discourage using rope - wish they had told me that before I bought 100m of nylon and spliced it onto the chain, only to find the gypsy cant work with rope !