One of the easiest ways I found setting most gaps is the use of a business card between the magnets and the coil legs as most are set very close .010" which coils are usually set at. Now .30mm is very close to .012" so that should be within the tolerance range though I don't know the specs on the Victa.
Also if the flywheel is hitting the coil legs check that the flywheel side crankshaft bearing/bushing doesn't have a lot play allowing it wobble as it turns. I have seen a few Briggs push mower engines with this problem.
Also there are places that the use of anti-seize will cause problem as you want the fiction of the fit to be there. Anti-seize also will throw off your torquing of bolts causing you to over torque them stripping threading.
