Acwally there are 3 main types,-
The 'Great' British (some say lash up) using either a combination
of Sierra 1800,Stag,Merc etc bits.
The 1st American 'tall block' which is almost exactly like your
RS lump with much longer stroke (only produced between 83+86)
and
The 2nd Tall block (87 on) which is more like a zetec (three bolt
engine mounting the same spacing as a zetec)but without the return
holes in the block which need sealing up on a zetec.