OK, I'm sick as a dog and home for the day and bored, so I thought I'd comment on your situation, hoping to get some feedback.
Sounds as though the stand has already been converted. The mature pines and oaks were cut, but perhaps the harvest wasn't heavy enough, which promoted the release of the tolerant hemlock and beech understory and the release and/or establishment of the relatively less tolerant red maple. Beech and hemlock are both climax species and unless removed will tend to perpetuate the same species. Red maple tends to be a pioneer species and may have been established in the larger openings created by past harvests.
Instead of a full blown stand conversion, over time can you simply weed out the unwanted species and try to promote the desired species? Some type of hybrid irregular shelterwood/seed tree cut where the white pine, red oak, red maple, and I'm assuming a smattering of birches is favored and the beech and hemlock are eventually phased out through timely cuttings and treatments such as hack and squirt? The time needed, and time is money, for a hack and squirt treatment generally prevents the practice from being popular throughout the northeast. But, if you are willing to provide the sweat equity then the hack and squirt becomes feasible. This may seem obvious to some, but I don't think anyone has mentioned that successful regeneration of white pine is highly dependent on the presence of a good seed crop and proper site preparation. Generally a shelterwood cut will provide the necessary shade to discourage the widespread presence of the weevil in pine, yet allow for enough light to promote adequate growth of the pine and oak seedlings and saplings, which are intermediate in shade tolerance.
Also, cutting the beech and red maple during the height of summer generally will promote much less sprout growth than a winter harvest will. During the winter the sugars and elements stored within the roots will be readily available for sprout production during the next growing season. A growing season harvest ensures that the majority of sugars and organic materials will be located within the stem of the tree and thus removed during the harvest. No matter how you attack it, remember that "white pine-no. red oak-red maple" is a naturally occurring stand type found in your area, so it may be beneficial to promote a stand that may occur naturally.
Without knowing all the factors it is hard to determine what would be best for the stand. These are the type of lots I hope to manage someday when I get licensed in NH. I like the northern hardwood stands and the mixed HW/SW stands, but there is something about a WP/RO stand that makes me drool. Maybe it's because we don't see many of them here in northern VT and NH. As a footnote, I have never seen the Brown Brontosaurus cut merchantable timber, but one morning we pulled into a sugar bush harvest we had in Easton, NH to find seven of the Bronto's on the landing getting ready to mow down the foliage that had grown up on an adjacent powerline. That was an impressive sight with those machines and the 7-8 skidders, feller-buncher, delimber, and slasher/loader we had on the landing.
