Its actually easier to breach Soviet base from upper edge. All what stands between you and soviet conyard there is single tesla coil and barracks. Also from soviet base direction it's easier to destroy War Factory - critical building for Soviets in this mission. Also that stops them from rebuilding.
Yeah I found out that you can get an easy time with by going over the upper bridge. Until you get to fight on it, they destroy it and you lose 6 tanks in one go :(
I did go for the outpost first, put rocketeers up, a group of Archons on the other side of that small mountain to deal with potential SCUDs. GIs and Guardian GIs in the small passage just to the left to stop anything from coming through. 2 or 3 of the 6 total snipers there as well and you can pretty much hold indefinitely.
Too bad you don't have that much time. I did find that an airdrop of ~10 Guardian GIs, 3 SEALS, 5 engineers, 3 snipers and some other stuff to make 24, near their south nuclear reactor does work well. Capture reactor 1, use some micromanagement to fight to no.2. Capture that as well and then take the con yard. Barely any base defences to kill and that gives the edge in attacking them. With that many units around, if they decide to commit to a fight, you're always standing still at best. Not a good place if you also have to attack some tesla coils.
Soviet SCUDs coming in is random. At one occasion they were mentioned before I could go to the allied outpost (even if I raced there with a rocketeer) and the second time they came around only when I started capturing nuclear reactors.