Hello Ben:
Suggest it was unlikely there was ever a plan to use helicopters for the Mussolini rescue based on:
- very immature state of helicopter technology in 1943, certainly the use of helicpters would be high risk, whereas....
- use of gliders for landing troops on precise locations was well established by 1943 e.g. refer the famous use of glider landed troops to capture the Eben Emael fortress in May 1940
Quite simply, why take unnecessary risks on what was clearly a very hairy operation?
I realise the danger of web-based sources, but this account does tally with what I have previously seen about the Mussolini rescue:
http://www.2worldwar2.com/otto-skorzeny.htm
Cheers
Don