Back to your question, the 1050 engines have become hard to find and rather sought after. I have heard of worn out engines needing complete overhaul selling for over $3000, and I paid that for a new one 14 years ago when the dollar was strong. A brand new motor in good working condition I think would fetch 2 times that amount or more.
If it has sat for that long though, it may have damage from storage. Does it turn over?
By the way, It wasn't too hard to put that motor in a Fiat 600 based Abarth car. The hardest part was drilling the crank for a pilot shaft bushing. The machine shop that did mine said the Abarth crank was made of the hardest metal they ever tried to drill a hole in. That motor also will not take the mechanical water pump fan assembly that was used on the 600's. I had to run an electric fan and a PBS racing water pump.
Goodness! US$3,000!?! I paid US$2,000 a couple years ago for my rebuilder, when the market was at it peak. A friend of mine has been offered no less than 10 short motors for sale recently at less than US$1,000. Given the current economic climate, prices are down down down.
With long term storage, one would have to assume the engine in question would need re-honing and a clean out to become a runner. Given that the Sportiva if Fiat 850 based (not Fiat 600), and assuming it is a 1050cc motor, to fit to a Moretti Sportiva it would need at least a sump (US$500-US$750), reverse rotation gears (US$500), valve cover (US$100), plus crankshaft machining, before fitting the Moretti carburettor, clutch and exhaust system. To control the cooling issues related to increased output, a thermostatic cooling fan (US$50), front or transaxle radiator (US$200), new water pump (US$300) and oil cooler (US$50)...it's not a small job. I know, because I'm doing it right now to my 850 Special!
Anything more than EURO$10,000 in the current economic climate is fantastic for the Moretti...jump at it, or hang it from your yatch. Check out Scuderia Topolino for the parts required, as they now own the rights to market PBS parts.