My two cents:

in basic gulliver game (SS.I vs 1 Bristol) I thimk the pidgeons have to rely in their superior fire power (9 guns vs 2).
IMHO there's two basic tactics to shot down a bristol in a such scenario: destroy his tail or reduce it to a flying brick with a few hit on its engine. So, take its tail and try shooting at him: his observer can shoot only at one of us.

If the bristol fly away by L3, S3 or R3, don't waste fuel in pursuing it... it's the Vulture who's looking for easy shoot, not us; wait till it's coming back.

And... beware the bristol stalls: a 0-distance shot from a bristol is a ticket for the pilot heaven