Canadaicon more or less set up for No 4 rifle production with a "green-field" site; they had no pre-existing SMLE works in place - fairly simple to go straight for the new factory for the new rifle.

I suspect that there was very little cash about in the Commonwealth coffers at the time to effect the changeover, and in any case the strategic picture, at least at the time that the No 4 factories overseas were being set up, was that the defence of Australiaicon would rest on "Fortress Singapore".

Once the futility of that notion became apparent, then it was too late to change over. The Lithgow factory was just going to have to churn out SMLEs as quickly as it could.