[9W Monighan]

Tom is correct and I'll try to add some more to this. Something I noticed on your shovel is, The hoist drum will need to be larger in diameter because the rope diameter you will be using has to have a minimum diameter it can flex around to keep it on when there's no tension and not damaging it if it wraps on top of another wrap because of too much crowding the dipper handle. There only needs to be enough rope on the drum for the dipper to make one complete cycle plus one or two extra wraps to keep the rope from pulling out of the clamp holding it on.
On shovels the hoist drum is tapered also. This taper speeds up the feet per minute through the hoist cycle because the circumference is constantly changing and gives more power where the most digging is taking place. Once you have the diameter figured out,figure out the gearing.