Just sold the only S1 block we had...Thought about converting to a S2/3 engine and transmission? easily done you just replace them as all the mountings line up and the throttle and gearbox linkages are the same. Problem is the S1 gearbox will not fit a S2/3 engine so you need a S2/3 gearbox as well. Another solution would be to have the block sleeve-lined see this link below
https://www.oldlanciaspares.com/372-lancia-APPIA-ricambio-canna-motore.phpWe have lots of spare S2/3 blocks as well as reground crankshafts, crankcases, cylinder heads and complete gearboxes.
Jim Appia Consortium manager