Identification solved and part on order.
Tony Bouchet at Extreme Limite has identified and is supplying the replacement pump, and the Venturi will live.
In case anyone comes across this post in the future with a similar problem: the pump pictured above is in the tank and is solely a lift pump to get the fuel from the tank to the main high pressure pump which is bolted to the engine.
We are not sure of the pump's origins (maybe E21 BMW?) but Tony has a replacement with the same fittings. The replacement is not identical and needs a new nylon(?) insert in the base of the ally tube with a different inner bore to fit the new pump. Total cost about 320 Euros. Be aware that if your pump runs, but no fuel is coming from the tank, the pipe that connects the pump to the top of the tank can come adrift, helpfully recirculating fuel about the tank. The pump can be removed from the nylon by carefully tapping it out downwards.
Then only the fun of replacing the fuel tank...