GREAT
Many thanks for your efforts
Some quick observations:
1.- You would need the older conning tower, AFAIK the Narwhals didn't switch to the cut-down profile during the war.
2.- I take it you will modify tonnage and maneuverability to better values? Narwhals were slow and bad handling, plus increased tonnage would also affect the ASDIC profile
Cheers
P.S. Do you need pictures or more info? I can look for some stuff in my archives and around the web