I like neutral toe so I have in the past just "sighted along the front tire" to get it dead lined up with the rear on one side, then adjust the other (ditto). Helps to park with the fronts on something slippery like a stack of polyethylene sheets. Not going to get you to a particular number (even if you trust your fancy angle equipment) but I can say the poor- boy method has gotten me decent tread life and handling on vehicles that didn't deserve more than that. And what more is there really?
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If the motor was rebuilt with forged pistons, those have a higher thermal expansion and are made with a higher cold clearance, so will rattle until operating temperature is reached. Bore wear could be a factor but ought to come with symptoms like oil consumption & smoke. Off-idle stumble can be from a too-lean main circuit "covered up" by a rich idle screw setting. Vacuum leaks can be a significant low-RPM lean contributor. If car has power brakes, use the brake pedal's "booster air surge" on apply, to see if running too lean (brake will induce a "lean stumble". A wideband AFR meter is a great tool for tuning carbs (essential for EFI, good idea for carb). You can get the main circuit jet / rod / whatever trued up at cruise, then adjust the idle RPM and mixture. A big cam will affect accuracy at low RPM but this is not mentioned. If all you need is a < / > stoich reading then a real cheap heated O2 sensor can be useful, you need cig lighter power and a multimeter. I've tuned mixture on cars from carb'd Chevy van to EFI Porsche 928 this way, back before WBO2 meters were commonly available.
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