what year/ casting number is the best to use - i know where theres a few flatheads sitting round rusting and though might use one of them for another project -

 

Bootie, there are basically no casting numbers that are in any way dependable on a flathead. Well there are a couple, but even those don't tell much. YOu have to learn to know what you're looking at based on physical description and location of bolt-on accessories. Check out this site and enjoy a long, long education.

http://www.vanpeltsales.com/FH_web/flathead_home.htm