I know this thread is a bit long-in-the-tooth, but figured I'd add this bit of info in for reference purposes. Having just picked up a MFK 700 I went through the various guide rail adaptors I have and landed on the Makita one being a perfect fit. It's this one (model number 194579-2):
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The smaller section comes with a foot so there's the option to use that should the need ever arise. The larger section is what goes on the rail, but, unfortunately, the rods don't pass through it and neither do the ends going into the MFK meaning cutting down some rods. If I didn't have other beefier routers that run on rails already, I'd be tempted to drill through the adaptor to allow just that. But, and it only just came to me now, I didn't check whether there's clearance for the rods to go all the way through the adaptor and clear the high spots of a rail beneath. And, yes, there's no micro-adjust either.
The rod spacing is for their RT0700 palm router which may well be the exact same spacing as other near identical palm routers from other manufacturers? A quick Google for "palm router guide rail adaptor" didn't turn up much besides the Makita one and one for Bosch rails though.