I have an old SuperV that I think rides awesome with my RockShox Psylo (5 in tavel). They don’t make it anymore but I would def recommend a fork with adjustable travel. The Psylo has U-Turn so I can adjust it on the fly. Your bike was made for 60mm travel (mine 80). Putting a longer travel fork on will change the headtube angle and will effect the way it steers. With adjustable travel you can dial in the amount of travel that gives you the best head angle for what your riding. Long travel slack angle good for steeps, short travel steep angle good for fast tight turns. It seems to all come together just as I want it with U-turn.
As for adapters you can get reducers that you put your own headset in (what I did) or you can get some that fit into the Headshok cups and bearings (if they are still good). Any LBS can get these from a good distributor not Cannondale. Have the shop press them in with a headset press or get a large threaded rod with 2 nuts and some big washers, grease em up and press them in nice and square. The HS crown race could be tricky without the right tool. It’s worth the cash to have the shop do it right and not damage the parts.