Hi
Glad you are not instantly horrified at what you found, probably normal for a £2k one of these cars now.
A full resto will be expensive, especially given your comments unless you do all the work yourself. If the door is bad, go for a n other if you can find one. The lower lpart is common to the Coupe, the difference is the upper frame.
Bonnets are harder as most do rot, especially along the front edge.
The sills are very common rot points as are the floors in the Spider, also check the A pillar inside the front wings, though hopefully you have the wing liners.
On my Spider the rear turrets were badly rotted out, mainly around the base.
Really odd to have a core plug missing (ice damage?)
You can check the engine code which is stamped on the block just above the oil filter housing. Your badge implies 2l which would make sense as most later cars were 2l.
My restoration is here (long) if you want to see what I found.....
http://lanciabeta.co.uk/forum/index.php?topic=1936.0Peter