The leg currently does not have a flame trap, how important is this to my engine?

I have a b21 with su carb and most of the emmisions system still intact.

The car had a elbow pipe with a vac line attatched, is it important that this vac line stay attached?( i broke the fitting)
So i have rerouted it for now. Since then, the car no longer stalls with no choke on, however, it smells like a diesel, not bad oil burn but you can smell it burning oil now.

Is it worth re-installing the flame trap?

We remove them on the old redblocks as they gum up.

You're talking about just the strainer in the nipple not the oil separator right? No concern about back firing with it being removed?

Yes the strainer, no concerns about backfiring.