I am not familiar with the "Fluidyne" wheel-skis that you refer to, however, in case it may help you, there is no change in the balance of a DHC-6 Twin Otter aircraft when wheel skis are extended or retracted. This is clearly stated in the DHC-6 Twin Otter AFM supplement for wheel skis.
If the "Fluidyne" skis are a product that was originally provided by de Havilland, there should be a supplement in the AFM that specifically addresses operation with these skis. If they are a STC fitment, then it is unlikely that there would be any de Havilland documentation about them - the STC holder will have issued an approved AFM supplement.
Viking Air in Victoria, BC, Canada is the type certificate holder for the DHC-2 Beaver. The company can be contacted by email, the email address is
[email protected]