Just poking around thru the fiche, it looks like the 79 RD400F, 80-81 XS400 Specials, and a few 250's got this caliper, and THAT'S IT. I didn't check Every bike from 60-80, but within 5 years either way of 1980, between the XS/RD lines, ONLY these few models got that particular caliper. How Bizarre.... I would have thought for a budget-minded line like the XS400 that there would be more parts-sharing.

hey mate have you found a caliper yet as i have one spare i bought for my 1981 xs 250 special works great but that was not my problem mine was i needed a new master cylinder if you are still after one i can sell it to you cheap would take about a week to get to you as i am in Australia say something along the line of 40-50 gbp i think the conversion is including postage