Will 250 and 332 coexist?
When my ties are buried under ballast I use standard code 332 rail and plastic ties. There is a variety on clips to let you join code 250 to code 332 rail. I do not think I will add more hand laid track but I’m glad I did where I did. I may add more code 250 rail with plastic ties because I like the look. Remember my time period is 1900 narrow gauge.
The section of track below has the ties glued to redwood strips underneath with "Gorilla Glue". This keeps the ties from shifting and sinking, you can glue the ties down and then spike the rails, this would probably be easiest.