In the book 'Nimrod's Genesis, RAF Maritime Patrol Projects and Weapons Since 1945' by Chris Gibson there's a proposal for a six engined Nimrod drawn up for the Royal Canadian Air Force.
A later version with underwing refuelling pods and a strengthened airframe was called the Export Nimrod.
Having built a few Airfix 1/72 scales HS/BAe Nimrod kits in the past there's not much in the way of ground clearance for the proposed podded engine concept and lengthening the undercarriage might be a bit tricky.
I have two model kits of the Airfix BAe Nimrod in the stash. (One and a bit!)
My idea is to extend the wings by adding an extra engine making this a six-engined beastie. Strengthening spars will be added to stop the wings from sagging and a raid in the spares box should reveal the Matchbox/Revell HP Victor refuelling pods.
I might even have a set of Canadian decals.