I don't really understand what you mean by "a complete high/low", I took it as a whole bar. Nevertheless this is what I came up with:

**[Opening Point of the Position]**

**Bar Opening**

**Enter the market at the beginning of the bar**

**Base price** - *Open*

**[Opening Logic Condition]**

**Moving Averages Crossover**

**[ A ] The Fast MA crosses the Slow MA upward**

**Base price** - *Close*

**Fast MA method** - *Simple*

**Slow MA method** - *Simple*

**Fast MA period** - *3*

**Slow MA period** - *50*

**Fast MA shift** - *0*

**Slow MA shift** - *0*

**Use previous bar value** - *Yes*

**[Opening Logic Condition]**

**Moving Average**

**[ A ] The bar opens above the Moving Average**

**Smoothing method** - *Simple*

**Base price** - *Low*

**Period** - *50*

**Shift** - *0*

**Use previous bar value** - *Yes*

**[Closing Point of the Position]**

**Bar Closing**

**Exit the market at the end of the bar**

**Base price** - *Close*

**[Closing Logic Condition]**

**Moving Averages Crossover**

**[ a ] The Fast MA crosses the Slow MA downward**

**Base price** - *Close*

**Fast MA method** - *Simple*

**Slow MA method** - *Simple*

**Fast MA period** - *3*

**Slow MA period** - *25*

**Fast MA shift** - *0*

**Slow MA shift** - *0*

**Use previous bar value** - *No*

Again, if I understood you correctly, the strat above buys like you stated, so to make it behave correctly for sells, logical groups should be involved. Final version then:

**[Opening Point of the Position]**

**Bar Opening**

**Enter the market at the beginning of the bar**

**Base price** - *Open*

**[Opening Logic Condition]**

**Moving Averages Crossover**

**[All] The Fast MA crosses the Slow MA upward**

**Base price** - *Close*

**Fast MA method** - *Simple*

**Slow MA method** - *Simple*

**Fast MA period** - *3*

**Slow MA period** - *50*

**Fast MA shift** - *0*

**Slow MA shift** - *0*

**Use previous bar value** - *Yes*

**[Opening Logic Condition]**

**Moving Average**

**[ B ] The bar opens above the Moving Average**

**Smoothing method** - *Simple*

**Base price** - *High*

**Period** - *50*

**Shift** - *0*

**Use previous bar value** - *Yes*

**[Opening Logic Condition]**

**Long or Short**

**[ B ] Open short positions only**

**[Opening Logic Condition]**

**Long or Short**

**[ A ] Open long positions only**

**[Opening Logic Condition]**

**Moving Average**

**[ A ] The bar opens above the Moving Average**

**Smoothing method** - *Simple*

**Base price** - *Low*

**Period** - *50*

**Shift** - *0*

**Use previous bar value** - *Yes*

As you can see I tuned the indis to fit your strat, the best I can achieve without custom indis unfortunately.