Thanks Brandon - If I'm swapping out those (TCC solenoid and MLPS & speedo gear), would it be better to switch to a newer tranny?You will need to swap your TCC solenoid and MLPS and change to the appropriate speedo gear for your tire size/rear axle ratio; the Mustang has an 8 tooth output shaft and the Mark VIII has 7. Most likely 19 teeth if you have a 3.08 (or 20 with a 3.27).
There are alternatives to the SpeedCal; however, I have not tried this unit yet so I don't know how well it works.Depending on your tire size you might be able to get away with a 3.55 with a 21 tooth, but 3.73 is off the table unless you want to get a SpeedCal because the 23 tooth gears are known to self destruct on a semi-frequent basis.
Apologies in advance for the stupid questions. I got a 4R70W from the '98 Mark VIII (I have a '95 Mark VIII). The (newer) transmission came with the harness.You will still need to...repin the harness. 🤔