ya, 240 and 260z have r180's in em, 280z's have r200 3.54 open diffs.
i personally like the 280zx's r200 because it's a 3.9 gear ratio, only second to the hard to find 88 300zx turbo 3.7 vlsd r200
and i concur,
www.hybridz.org is a great site, i'm a member there as well
gl
Dave