first get the priorities straight. forget brake discs, super duper spark plugs etc.
Get the car in good service condition, sounds like your engine is a dire need of a thorough tune up, change engine, gear and diff oils, Diff and gear takes GL3 or GL4 SAE 90 gear oil; adjust tappets to correct factory setting to 0.20mm inlet and 0.30 mm exhaust - HOT ENGINE.
cold setting is 0.12mm for inlet and 0.22mm for exhaust, remove distributor and open it up, clean and grease the centrifugal advance mechanism and make sure the vacuum advance is also working - repair as necessary, replace contact points and condenser and set dwell by using a feeler gauge of 0.40mm between the distributor cam and heel, it should be a neat sliding fit.
Clean and adjust the carburettor and have an 850 rpm idle speed - not less otherwise you will be scratching your head to make it run smooth. Install the original thermostat valve in the engine to make it warm up to temperature. ENJOY.. the mighty simplicity of the car.
btw - correctly pack the wheel bearings and adjust the brakes, they will work nicely. You can try to jam a KE30 or KE70 spindle (king pin) in there but it doesnt work, you will hate yourself after youve done with it.