I love the style of these, watching with interest
For info / pics / curiosity etc, I've just noticed an advert for a 403 Estate (UK, £4,500 or offers)
www.carandclassic.co.uk/car/C1009352
No engine swap .. Maybe you get away with the 58 BHP engine from a later 403.....it looks the same.
www.carandclassic.co.uk/car/C1009352