Hmmmm.
Might want to check the distance between the axle and the dropout hole on both bikes and see if they are different. Just a small difference at the mounting hole for the RD can make a big difference at the big cog.
In my experience, 28 with an NR RD is always a bit of a stretch, while the SR RD seems to do it more easily.
If your chain length is set at big-big plus a linkset, it should be correct for this application. What happens when you try to shift into big/big?
Too tight? Skates across the freewheel?
What kind of freewheel are you using? When trying to use larger freewheels, have always had the best luck with mid-late 80's Shimano UG series. Now that I think about it, also used 10 tooth Shimano pulley wheels on the RD.
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