Rear wheel cylinder refresher

["nruff" <nruffcorn@prodigy.net>]

Can some-one help refresh my memory......I searched listquest but with no
avail.  The rear wheel cylinders from a 510 appear the same as the
roadsters, but are different/won't work because why?  They are obviously
very plentiful as every parts store can seem toget them while they don't
even list a 311.....wonder why <g>.

Thanks
Nathan