Not sure about documents or the DVLA. On paper you will ned to pay import tax (since Brexit) on a car under 30 years old. This would be 20% of the purchase price, but as you will be getting the car for free, not sure how that would work.
Insurance is no problem, there are plenty of people driving cars in the UK that were never sold here. Look at insurers of the type advertising in classic/American/kit car magazines (or Auto Italia in your case).
The tax would be based on its emissions and age, same as a UK car. The figures I have say 199g/km which would be £346.50 if paying by direct debt over 12 months, £330 if a single payment.
If you do decide to get the car, I'd strongly suggest joining a Lancia club. It will be an invaluable resource for advice, spare parts, etc
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