[Heroka Vendile]

There has only ever been one Leman Russ model produed by GW, thus it is still the ubquitous Mk1 chasis (as designed by the Primarch Leman Russ himself *cough*), mearly updated and tweaked into different patterns (i.e the origional Mars pattern, Alpha, Ryza, etc, etc.).
Taking this into account, a particular Leman Russ may be a Mk1 chasis, but with a Ryza pattern turret on top.
With this turret it could also be presumed that the patterns made by each forgeworld will evolve as well, thus this Mk1 chasis might have a Mk2 Ryza Pattern turret.


I may have over-complicated that, so think of it this way:
A Land Raider Crusader is still a Mk3 Land Raider, but it is has a Crusader pattern weapons outfit instead of the nomal one.