Removing paint

[Canadian Atlantic Railway]

I have several Walthers two bay aggregate hoppers that I stripped awhile ago but some paint was left on the outside on both ends of the cars. It is hard to get anything in there to scrape and I came across a grit blaster I had bought and there was some unknown grit with it. What would be a good medium to use with the blaster that will take paint off but not eat into the plastic?