Thanks for this advice! Yes, I thought about the styrene option, but I wanted an easy fix. 

I'll consider these options in the project!

I have a Big Hauler 4-6-0 that is missing two parts that are out of stock. The hatch on the cab is missing, and the number plate on the front of the smoke box is missing. Would these two parts be suitable substitutes?

Roof Hatch for 2-8-0:
https://estore.bachmanntrains.com/index.php?main_page=product_info&cPath=69_142&products_id=5005&zenid=0sp2unnerjb8vt8hq75vul0uh5

Number Plate for Two-Truck Climax:
https://estore.bachmanntrains.com/index.php?main_page=product_info&cPath=69_641&products_id=8315&zenid=0sp2unnerjb8vt8hq75vul0uh5

I know the number plate would not have the right number, but I'm not picky about that.

I'm particularly interested in knowing if these parts are approximately the same size. Thank you!