Recipes like those should be treated as a conceptual starting point or examples.  They have to be adapted to your situation.  We cannot help you adapt it to your situation because we don't know your situation.

However, having said that, with a Gilbert mixer, you generally use a square wave to drive the LO, and there is no reason from a simulation perspective to avoid square waves as long as you are not using harmonic balance.  If you are using harmonic balance, you should switch to using shooting methods unless there is some strong reason to remain with harmonic balance.  In that case you should crank up the number or harmonics associated with the LO fundamental.

-Ken