If your vehicle has an original B stick to it. 3B will not make your life better in terms of Power and noise both. We have a lot of FJ40s around us but the original BJs are getting rearrer so keep in mind that.
Just get the engine overhauled by a good mechanic get evry mecanical thing in order and forget it for 10 years.
If you still want to change the engine then there are other options.....B to 3B doesn't make sense.
P.S. If possible Kindly post the pics of your ride in detail.