The plant is responsible for upgrading the planes from MK to M2 standard. More details about the Syrian Su-24s undergoing this upgrade can be found here.
The photo seen above shows personnel of the 514 ARZ plant working on Su-24 serial 3506. Su-24 3506 is one of the twenty-one Syrian Su-24MKs being upgraded by the repair plant in Rzhev.
514 ARZ also removed the direct link. (13-1-2014)
Yet, the author still has printscreens of the site while showing the Syrian Su-24.
Syria's recently upgraded Su-24s (1)