The Slater's crankpins can be modified by using 10 B.A. machine screws and nuts in place of the supplied 12 B.A. items and tapping the bushes and bosses 10.B.A.
Markits supply what I thought were 10 B.A. crank pins and bushes, the last lot turned out to be metric 1.6mm.
Derek Mundy does a nice heavy duty turned item.
You can of coarse turn your own if you have a lathe.