We cut about 100 acres of pulp wood the contract was for everything 5"-36" in diameter to be cut 6" off the ground or lower. We used modded 441's, 361 and even a couple of modded 660's with 20-24" bars and we had 3/8" full skip semi chisel on them all.
That chain is slow to dull and fast to sharpen. Make sure it is Stihl chain, as that lasts the longest of all chains in harsh conditions. We used Stihl ES bars with roller tips, which had no problems with that.
One suggestion though, don't know your finacial situation, but you will be time and effort ahead if you just get a bigger dozer than is needed in there and in a few days it will all be over, root balls and everything. Otherwise you are just making a nightmare for yourself, by cutting the tree off and then getting the rootball out later, that is just a bad idea, typically.
Again, pay more per hour for a too large of a dozer to get in there and they will save you hours and hours of poking around with a little "proper" sized dozer.
My $1.50 on the project,
Sam