Here is a simple 2:1 gearbox made with steel gears and aluminum housing. This is used to reduce the speed of a trommel on our homemade gold wash plant.
an easier way to get the bearing on instead of hitting it and potentially damaging it is to take a 100W light bulb, set the bearing on it for oooh about 1 minute, then put it on the shaft. It will slide right on and then cool and compress back! It doesn't need to be nuclear but just hot enough that you'd rather not touch it with bare hands (about 130-140 deg)
how much did it cost you to make this gearbox would it hold up to 80 Hp I need a small reverse rotation gearbox like this one with 1-250 shafts out each side with 1/4 key on the out side of them could you tell me if you might build one and what it would cost thanks. also I need it to be 1 to 1 I would like to use Quick change gears can you make this thanks.