Yes it will.
I had a 235 in my '52 GMC with a 4.56 rear end, and I managed an absolute top speed of 72 mph. However, I always cruised it at 65 mph which translated to about 3200 rpm, if I remember right. A 4.10 gear should add at least 5 mph to that.
It's hard to say if it's worth it. You should see if you can get a guarantee that if it's bad, you can get a full refund. Then pay a shop to check the gears out for you and change the ancient oil.
