Best fasteners for std coupe rain gutter?

[alexiskai]

One of the rain gutters on my '29 standard coupe is starting to come off the roof. I can see where there are a number of holes and even a few tiny nails still in the gutter.

Does anyone know the type and size of nail or screw I should get to reattach this? I went to a hardware store and looked online but all the options either looked too big or too small. I'm also not sure how long the nail could be without coming out the other side of the wood.

Thanks!