Help/Advice needed for soil stack

[SunnyDunny1]

I am planning to run a sink and bath waste into an existing soil stack
The only place I can achieve a decent run down is if I connect below the toilet feed - I am concerned that the smells will vent through the sink and bath or will the u-bends on them be enough to stop?

Not that I think it makes any difference but it is a cast iron stack and I will be using a timesaver bosswith 40mm pvc

 

[seco services]

the traps on the bath and basin will stop the smells coming back up the wastes.