Great looking 300. I have one that I bought, but it was sick when I brought it home. I too added an electronic ignition, new seat, hydraulic hoses for the lift cylinder, and then a camshaft. Mine would run fair for a few days, then like crap. I scratched my head time after time on what the problem was. I lashed the valves, checked the compression, set the timing, but finally tore it down and found the cam gear in pieces. I installed a used cam and it solved all the issues I had.
My 300 is my go-to tractor around here, strong and always starts in the hot or cold. It still has it's work clothes on. Yours looks great...