I traded my R56 for an R52 recently and as far as I could tell they're very close. If anything, I think the spokes are rounder in cross-section on the 1st gen and somewhat flatter on the 2nd gen.
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R53
R56
Obviously NewMiniStuff have worked it out. Perhaps you can offer to purchase the parts from them if they are willing to give you hints about what modifications are needed. -
BTW, if you want a steering wheel to ship to England, I upgraded mine to JCW and have an extra 3-spoke in excellent condition that I can sell for cheap. There are probably plenty of them lying around from people who got the JCW steering wheel.