Interval work certainly does carry over to endurance events. Although it couldnt hurt to have a longer (longer for me is 3-5miles) run every other week. Swimming, well you need to practice swimming as that is a completely different monster. Biking is pretty easy compared to the other 2. Great job and good luck!
Just rememeber....the studs are probably 20lbs lighter (or more) and only focus on endurance. Had there been a deadlift station in the middle of the race, it might of been an equalizer for you. While I do some adventure races and tri's here and there....I never really train hard core for them (i am not going to run sub 6 min miles anyways). Just do it for fun....enjoy it.