The '98 Mark 4R70W is more desirable; if you are going to make the swap I would try to upgrade to some or all of the parts that changed in '98. Honestly the Mark guys like to upgrade to the earlier 2000's 4R70W. I don't have any specifics in front of me but I can dig them out if someone doesn't beat me to it.
Yeah cause I got a 97 mark 8 sitting with a brand new tranny but the PATS system screwed it up and now it's wont run. So I wanted to just take the tranny out and throw it in my sc