Fitting AK47 Gas Tube to Saiga .308

As I'm sure you know, I've been working on my Saiga .308 as of late. Now, I'm on the point in where I need to hand-fit my new gas tube from CSS (http://www.carolinashooterssupply.com/AK47_Saiga_Vepr_gas_tube_handguard_upper_gastube_p/ak47-gastube.htm). I've filed a bit down from the ramp towards the front trunion and a bit from underneath, and I still can't get the tube to lock down properly. Does anyone have any suggestions as to how much and where it needs to be filed? I've looked around the internet and around other ak forums, and the most descriptive images are locked behind a subscription fee. http://imgur.com/a/lbkVR

(edit: added photos)