Do you have any history regarding the engine? A crank with three keyways is really strange.....there can be two separate keyways in line but, if there are three key slots cut around the crank, something is amiss. Also, breaking a key in shear (one half is still in the crank and the other is still in the balancer) is also an indication of problems greater than just a key...... a key is a mechanical fuse that breaks because of some greater problem

If your engine is hooked to an automatic transmission, you can probably remove the crank and ring gear combination if the oil pan can be removed. However, with the problems encountered so far, it would be wiser to pull the engine and find/fix everything. You can rent an engine hoist for peanuts.