Two biggest parts are the driveshaft and kickdown linkage.
By the way if you are running that low of horsepower would it not be less expensive to stay with a 904? There is a lot of manufactures that make performance parts for the 904.
I have done a bunch of 904 and 727. By the way I am definitely a 727 guy (had to mention that before I get ration of crap from all of my friends) If going to a 727 the driveshaft is probably the most expensive part unless you have one. You can run a manual valve body and then you do not have to worry about the kick down linkage. You did not mention what rearend you have. Most of the time when people upgrade the transmission, they already have an 8 3/4. And save that speedo gear you are going to need it.
