At the risk of horrifying the less technically-challenged and more competent craftsmen in the JRA, I, somewhat hesitatingly, offer my bodge-up solutions.
David T, (Pom, not Kiwi) quite rightly, told me to get my partners tapered when I had them welded up. (Why did I go for stainless steel partners in the first place, you may well ask. Dunno. Probably because I didn't trust my woodwork to make wooden ones.) It was a shockingly expensive choice and the wrong one, too, because the metalworker, when he realised how much it was going to cost, said that the additional time involved in making it tapered was going to mean I'd need to take out a bank loan to pay for it. However, I ended up with a parrallel-sided mast in ditto partners. I had the mast out a few months ago and with a little help from a friend, put it back with foxed wedges, ie one from top and one from underneath. This did a pretty neat job and I then dribbled some Gorilla glue around them to keep them in place. Seems to work perfectly, even if it's not the most elegant solution.
The mast step is a much snugger fit. I put lolly sticks (popsicle sticks/small tongue depressors) vertically around this. After the first couple of sails they worked into place and I added one or two more until I couldn't fit another one. The mast step is lined with some thick, hard, black plastic (don't ask me what exactly) to obviate (I hope!) the risk of corrosion between mast and partners. All very satisfactory and, as the lolly sticks are around the forward side of the mast, inoffensive.