Actually that's wrong,....very few of the 4.1's came with 8445 heads.
There are some differences between the heads. I don't remember specifically but it was something about the ports being a little bigger or something. Maybe somebody else can chime in.
I am curious as well...what are the differences? Is there any benefit / drawback to using the 4.1 liter 25506293 casting heads? Do they have to be milled down any? I read somewhere the deck heights were different, is this true?
The only disadvantage of the 6293s are some didn't have bridged water passages. Mine do. The ports look almost identical. I think the only other difference (and I haven't confirmed it yet) is that the 6293s use a different thread for the accessory mounting bolts.