A28 is a casting code used by GM. A=January, 28 indicates the 28th day, so it was cast on January 28. The E and C could be identifiers of some inspector or shift leader. I doubt they indicate anything functional nor important. The three cracks you've shown there in my opinion would kill that flywheel. Any small cracks won't matter and generally will go away when you have it re-surfaced. Any crack large enough to put a straight pin or the end of a sewing needle into...please avoid using that one. As for the 216 flywheel, you can do that however I believe you will have to use the 216 bell housing and starter. Or, somebody here probably knows...maybe you could use the different starter gear ring that was used on the 235. The flywheel itself will bolt right up, however.

~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end