For the guardrail caps, use SR_1tBrg_w_005mEnd.s

C = Concrete, W = wood, Y = yard (dirtier ties with more gravel on the ties) but there's also a shape difference -- the C's have a gully in the center of the ties like you see on concrete ties, so depending on what you do with underlying berms/terrain, there might be be a noticeable difference on the ties.

The nice part of Scalerail is being able to mix textures. On one of my mixed CNW-MILW routes, I use "C" tracks for the MILW with a gravel/cinder type ballast and MILW switchstands side by side with "W" tracks using Pink Lady ballast and CNW style target stands.