You will need to change flywheel and bellhousing over as well for Spider engine to go into Alfetta.
Regarding the Alfetta engine into a Spider or other 105/115, most of the 2 litre cranks I`ve seen have actually had the end drilling for the pilot bush. Alfa were making the 2 litre twin cam for 2 chassis types for the whole of the 116 production span, and I think most cranks were drilled anyway not being specifically designated at that stage of the production process to a particular block and ultimate engine placement.
i have a spider engine in my 77 alfetta sedan. there are differences in where the air pump is mounted, and then also how the hose runs to the exhaust mani. it goes around the back of the engine on the alfettas but goes from the closely mounted pump directly back to the manifold on the spiders. my alfetta just uses the spider parts so everything from the donor engine will fit ok.
I have yet to see a stock Alfetta motor with a crank drilled for the pilot bearing.
There is a minor difference between the blocks, A Spider block is drilled and tapped for the oil pressure light switch on the exhaust side of the block and an Alfetta isn't.
With the proper tooling drilling the cranks isn't hard. A couple of years ago I took 2 or 3 'fetta cranks over to a buddies shop and drilled them all for pilot bushings in about an hour total.