Hi Grandpab,
I recommend this chassis and it is on sale for $55! It does have the Walschearts valve gear. It also has the reliable smooth running Vaesion 5 chassis. Here is the link:
http://estore.bachmanntrains.com/index.php?main_page=product_info&cPath=66_69_623&products_id=4085The difference between this and your Blue Comet chassis is that the wheel centers, steam chests and pilot will be black rather than the blue. You will be able to use the pilot wheels and the pilot(cowcatcher) from your old chassis, but would have to paint the steam chests and driver centers yourself if desired. Your old steam chests will not transfer tom the new chassis.
Have fun with the project.
Loco Bill