I have a triple crank I want to pull of a my road bike before I sell it and throw a less expensive double on there. The rear derailuer is a long cage for triple cranks and the front (friction) is for a triple is well. Do I need to be concerned at all about making the switch?

I have a triple front and rear derailuers on a double crank right now, the only thing is that you have worry about is to set the high/low limit screws just right otherwise your chain will DEF derail. The limit screws on my front derailuer are barely long enough to set the swing just right. I am using Dura Ace STI, with DA front and rear deraileurs.....all triple. But there shouldnt be a problem unless i am overlooking something. Also, the bottom bracket spindle might be a little longer.....someone else with have to give you the details on that situation.

If it's friction shifting, just set the limit screwds where you can't throw the chain off.

That's kind of screwing the buyer.The double crank needs a shorter BB for proper chainline.