Just a couple of points Kieran, aimed at getting your engine running properly. First, because the breaker gap was too large rather than too small, your engine has been tuned by an incompetent, it can't have been a result of wear or neglect. That has implications for the whole engine, and the whole tractor. You have to check for abuse as well as deterioriation. Did you repeat your spark check after fixing that fault? There is still a possibility of weaknesses in the kill wire or the coil itself. It makes sense to fix each area you work on, not just stop when the engine runs a bit.
Second, I hope you cleaned out the fuel tank when you replaced the fuel hose, and verified that it has a genuine Briggs vented cap on the tank. That eliminates another whole source of future problems, and simplifies your diagnostic procedure.
Third, can you post a picture of the carburetor so we know what kind it is please? Also post the entire sequence of numbers from the cooling air cowl so we know the model, age etc.
Fourth, did you check the tappet clearance, and perform the oil-in-the-cylinder compression test, yet?
Fifth, when you unstuck the starter sprag clutch balls, did you clean it out properly so it will keep working? There must be no trace of lubricant whatever on the sprag, the balls, or the compartment the balls occupy: they have to be degreased carefully and dried. After cleaning the spindle bearing where the sprag runs on the crankshaft, it must have exactly one drop of high quality oil on it.
I haven't commented on what you are doing to other parts of the mower, because as you know yourself, you are not fixing it yet, just making it operate, sometimes by crude methods.
