The front end accessory drives can be a huge PITA on these engine swaps, so your mechanics may be speaking from personal experience. The best way to keep bad things from happening is to get EVERYTHING off the same year engine. By everything, I mean balancer, timing cover, water pump, crank & water pump pulleys, and all mounting brackets for the alternator, PS pump and AC compressor (if your Skylark was so equpped). If you don't do this, you can easily go nuts trying to find drive parts which will work together.
There are a couple of parts compatibility issues to watch out for, and they hinge mainly on whether you are running a long or short water pump. The water pump change was sometime in the late 60s - I think around 68 or 69. You can run either water pump on any year 1st gen engine. That is, the pump will bolt onto the block and work. However, with a short pump you will need a left side exhaust manifold with mounting holes for the alternator. The long pump will work with any exhaust manifolds, but then you will need heads which have accessory mounting holes on the end of the head.
If you aren't very Chevy-oriented, some of this may not make a whole lot of sense right now, but it will once you start looking at parts for the engine. If you are unsure of what you might need, ask here before you lay down any money for parts. If you can't get adequate answers here for your questions, I recommend that you visit a very good Chevy board called Chevy Talk.
The other annoyances you will run into are mainly wiring-related. This is because some electrical components are located in different places on the Buick and Chevy engines. An obvious one is the distributor, but you also need to accommodate the oil and temperature senders, and possibly the alternator. Short pump Chevys mount the alternator on the left side and long pump Chevys mount it on the right. The good news is that Chevy and Buick starters are both on the right side, so you shouldn't need to do anything to the starter wiring or battery cable.
Good luck with your project, and please keep us posted on how it is coming along.
Ray