At 86kg it would be reasonable to put the hounds high (somwhere between the middle and the top of the range).

Ronstan and Riley make the fittings but they are not the only ones. Most chandlery shops will stock them and many have the machine to attach them to the wire.

I just looked in the Whitworths catalogue and they only seem to have balustrading fittings which they call "Roll Swage Terminals". These are way too cheap to risk using on a boat so I would avoid them.

The Ronstan ones may be overpriced but they are certainly very expensive. Last time I looked it was $60 for one terminal. In practice, for Mosquitos these fittings look neat but are not necessary at all.

The standard swaged ends with a thimble will do the job, and you can do them yourself for a fraction of the cost. The tang for the top-end diamond fitting will work ok as long as it's positioned right. If building a mast I would just leave the diamond tangs till last and then put the mast up with them sticky-taped on - then you can move them around until they work.