Is there any reason to think that going into one of the 'Legacy' -60 communities would be a career hurdle? I've gotten somewhat conflicting reports on the prospect. I've heard that the time spent in the transition makes it harder to stay 'on timeline' career-wise, but others have said that its really not worth worrying about.
Could there be an issue; yes. Should there be an issue; no.
The problem could be if your squadron is due to transition when you have about a year left in the squadron. Once you get inside that year, it becomes a personnel managment issue since the squadron will start to look at who will be around for the next deployment (assuming you go Airwing HSC/HSM), so if you will not be around, then they may elect to roll you early vice transitioning you. It is possible (remote, but possible) that you could end up with a 'short EP' on your first tour if that timing really works against you.
If you end up at an expeditionary squadron, then you don't have to sweat it since deployments will occur more often for that squadron as compared to an Airwing squadron.
Usually squadrons will extend personnel to make sure they don't totally screw over a guy, so while it has happened, assuming you hit the ground running and do a good job, you can expect the front office to protect you by making sure you get an appropriate fitrep prior to departure.
Back when the HS guys went from H-3's to H-60's there weren't many issues and right now there is no stigma for the F/H guys going to the S. (Of course when we had to listen to the H-3 guys tell us how the Mighty Sea Pig won the cold war, it got a bit annoying...)
If you go HSM, then the B to R transition should 'painless' on your career. This was not always the case. Back when HSL went from H-2 to H-60B there was lots of blood on the floor from guys getting 'shot' when they were told as first tour JO's that they would NOT transition to the 60B. This basically limited their shore duty to the HT's (couldn't get FRS instructor orders if they were not 60B qual'd already) which made it tough to break out and get command. (Nothing against the HT meant by that statement. It's just that many guys who want RAG orders couldn't get them because their squadron didn't transition prior to their PRD)
So, don't sweat it, do your best and be the best officer and pilot you can be and your front office should look out for you if the squadron transitions at a time that is not exactly beneficial for your career timing.