I had a set of Commando peashooters made with 40mm inlet so they'd fit to the original double skinned header pipes without adapters. This firm is in the UK, they ship globally but it might be expensive these days with tariffs etc.....
https://armourmotorproducts.co.uk/exhausts/silencers/silencer-norton-peashooter-commando?filter=15
Like this -
https://armourmotorproducts.co.uk/exhausts/silencers/silencer-norton-peashooter-commando?filter=15
Like this -