I think it's already clear that a 42" on a 372 is a bad idea, but if you must press ahead with it, you either seriously hate yourself or the saw. At best it will be very slow cutting and hard on the saw. Your clutch won't like it much, and you won't like how slow it is. If this is for a couple cuts a month, maybe you could stand to tolerate it, but it certainly isn't a good combination for anything resembling even infrequent use. A 395 or 066 has to work to pull that much bar in the cutting you describe, let alone a 372.
In short, either get a bigger saw, or a shorter bar.