Some early Minis were fitted with the optional fresh air heater, with the air intake snaking through the engine bay. It was a bit of an afterthought, and makes the engine bay quite crowded.
Since we have a brake booster and a radiator expansion bottle, we’re going to need all the space we can find. Later models moved the fresh air intake to the right side wheel arch, which seems far more sensible. Using parts from a later Mini would be equally sensible, but far less fun than making my own ducts.
I’ve made a polystyrene former and wrapped it in fibreglass with epoxy resin. Once the resin was set, I chipped out the polystrene, then used paint thinners to dissolve any remaining pieces.