The parts manual for the WF-4 and WG-4 is on the Wizard site here. about half way down is the parts manual free. The post right after it, is how to convert the part numbers into the last current mercury part numbers.
The instructions given for the operation of the WD-4S motor are good for the WG-4 also.
Use TC-W3 two cycle outboard motor oil in your fuel no thinner than 32:1 mix ratio. Some on this forum use 16:1 mix and others use 24:1. If your motor has needle bearings, I think 32:1 is just about right. Use more oil if yours uses brass or bronze bearings in the power head.
You can get hard to come by parts on eBay by searching "Wizard outboard" and being patient. Lubriplate 105 is used in the lower gear case and is available at Napa auto parts if you happen to have a store locally. Corn head grease is a substitute for lower unit grease also.
The Wizard WF-4 has many parts in common with the Mercury KD4.
If your water pump impeller is bad, you can get a new one made by Bob Scott.
You will probably need the one marked "MERC KG".
You will need to send him the metal core from the old impeller. His contact information is here. Bob is a nice guy. just remember that this is not his main job and he does it out of love for the old motors.
The ratchet installed on the crankshaft for the missing (in the picture) recoil starter assembly is of the type for a WD4S. We do have a replacement carburetor main adjustment screw knob in stock if needed (http://fergusonpoolemarine.com/fuelsystemparts.html), and many other (Wizard WD4S) parts as well. Very cool to read that it was passed down from your grandfather.