You'll be taking them in and out quite a lot, so cut them long - mine are about an inch too long. That means you've got plenty to get a pair of pliers around to pull them out. If they're too short to pull out with pliers, you'll have to use a hammer and pin to knock them through (as you'll have to do when the gun is finished, if you ever need to take the barrel out again). You want to avoid that if possible, as you risk damaging and opening the pin hole in the wood each time.
Even though you'll eventually be shortening one end of the pin to fit, it's worth carefully filing both ends of the long pins after you cut them so they don't damage the pin holes by having jagged edges.
You may encounter different resistance over time as you remove and replace the barrel - according to humidity etc. A pin that was hard to remove is easier, and the reverse true for another pin up the barrel. I was dismayed when this first happened but then realised it's give and take down the barrel and it usually remains solid in the stock.