Well these models may not be strictly old school, but I reckon the FW designers for the new Horus Heresy figures have remained true to Jes Goodwin's original design concepts from back in 1990 for Space Marine armour variants. They just feel more military-like without all the skulls; scrolls and other assorted tat that modern 40k marines seem to blu-Tac onto their armour.
As such I would like to present my new (old) Sons of Horus tactical squad in MkIII Iron Armour.
There are more photos on my blog and also a full painting tutorial for any who may me interested in creating this obscure shade of green on their models! The link is below!
My Retro 40k blog can be found at the link above - Enjoy!