I'm affraid the nose dome is just one minor part of the problem: for a S61N one would have to stretch the fuselage; the part between the engines and the cockpit is longer on an S61N than on the SeaKing.
Besides that, the sponsons on the 61N are different (bulkier) than those on the Sea King.
To top it all off, don't forget the extra windows and the 61N- tailfin that has a different angle than on the Sea King.
There is a 1:72 S61N conversion kit, but it's very expensive and imho of very poor quality.
I've read a rumour by one of the guys from Whirly Bits conversions that they're thinking of an S61-conversion.
I hope I have not ruined your day, good luck anyway!
Gertjan