On a steel frame the wrong width isn't a dealbreaker, but if you spread the frame or fork, the dropouts should be realigned.

Also, 'having a lot of adjustment in your dropouts' won't help a bit with brake reach; that's all about the slots on the calipers.

And this will decrease the mechanical advantage of your brakes. You can fit a long-reach dual-pivot on the front to get acceptable braking, or fit a 700c fork and a normal DP brake.

Use a single-pivot if you want, but IMO even the best ones aren't quite up to front duty.