I think we would all be making an educated guess.
Im guessing , not as many as you might think. Out of around 126000 rifles and actions, and taking into account the English Trades uptake( accounting for most), and the factory production is various calibre's like 404 ( most probabley to Africa), 8x75, etc....I figure less than 2000, just my guess though..

Wanabebwana...that looks like a rebarrled / rebored Rigby????

Best
Eric