My track is made up of code 332 rail, on plastic ties, so using code 215 for guard rails looks good for my purposes. With code 250 rail, you could use code 215, but to get smaller rail for guard rails might be a big problem, unless you tried some O scale rail.
I used Mico Engineering spikes to fasten the guard rails to the ties. My bridges all have Garden Metal bridge ties (Plastic). I simply drill holes in the plastic ties, using a drill of a size that the spikes are tight in, in a pin vice. There is no problem bending the ends of the rails…don’t forget that the guard rails usually run at least part of a car length past the ends of the bridge. I don’t attempt to spike every tie…I think I spiked every sixth tie, if I remember correctly. All the guard rails have been in place for more than 5 years, without any problems.
I hope that this will help…
Fred