Casting numbers?

Could some one tell me or direct me to where I can find out what theses numbers mean 3898920, GM-5, F-29-3, They are on the heads of my smb.

I looked it up through www.mortec.com and found it to be a 1972- 1973 350 but, I could not find your exzact number I only found 3998920 so, recheck ur numbers cause that first 8 could be easily mistaken for a 9 on a motor that old.

thanks for the info, much appreciated.