904 to 727 conversion crossmember

a 904 is about an inch narrower than a 727 so the torque shaft for your shifter will be too long if you use the 727.It also has a lower mount.You can force your 904 piece in sometimes and although it's crooked and binds sometimes they work but aren't correct.Sounds like you are determined to use the 727 so you should shorten the shaft about an inch and fanagle the trans. bracket lower.
i also use a 904 behind my 340