Right, the good news is that the 9/32" rod only has a tiny bit of slop in the fence, and once locked down with a knurled screw or bolt it's sufficiently solid that I suspect the margin of error in use will be my (lack of) skill rather than the fence moving. As such, I should only need to grind down ~1cm of the rod to 1/4" for the thread - much easier than modifying a longer length.
Incidentally, I ordered a number of knurled screws from here http://www.wdsltd.co.uk/product/3333/kn ... el-wds-521. The M5 ones work perfectly on the fence (for locking the rod), so whilst I assume it'll actually be a UNF thread like the main body of the plane, it's appears to be fine.
