I don't think Arun went through the route you're talking about taking...
I believe he went from Vlad to Ulan Ude then went south to Ulaan Batur. He drove back up from Ulaan Batur to Ulan Ude and then went towards Novosibirsk via Russia, NOT Western Mongolia.
The route you'd like to take has you coming South from Novosibirsk trhough Barnaul and the Altai, to Olgi...in Western Mongolia
Once you leave Russia, the road will become a track(at best) and you will be able to get to Olgi in a 2wd van, but you better not be fully loaded. You don't need 4wd...what you need is really strong suspension. Make sure you have have that, your steering system is in good shape and all you wheel bearings are in good shape.
Once in Olgi, Blue Wolf tours is the company that's reputable...there's also a new ger camp, next to the radio tower...you can't miss it. They may let you park your van there...but I can't vouch for security. Mongolia is a very poor country and people may take things out of necessity, not out of greed.
In order to do what you're attempting to do, you might be better off riding to UB from Olgi via the Southern loop, and then taking the Northern route back to Olgi...OR a flight back to Olg(you can sell your bike to Rene at Oasis). The road from Ulan Ude to Novosibirsk isnt' as interesting as the Northern route back...