To get the machine ready for the retrofit, I first read through a three part series from Home Shop Machinist about Boss retrofits:
I found a lot of valuable information there. However I didn't do things the way the articles suggest. I ended up removing ALL of the old electronics and power supplies. The only thing I left on the machine was the stepper motors and limit switches. I didn't even use either of the cabinets since they are so much larger than what is needed (or at least what I needed).
For now, I am using the wiring that was already attached to the stepper motors and limit switches. Although when I package everything in my smaller cabinet, I'll replace it because the stock Bridgeport wiring is not shielded. Though I used the cables, I hooked them up differently. The limit switches are now set up as normally closed and I wired the motor coils to be in parallel (the third article, above, has a diagram that tells how to wire them).
At some point, I will also replace the old Sigma steppers with modern high torque steppers. Back when the original motors were designed, microstepping was not yet invented. As a result, they were optimized for "full step" torque and are not smooth with a sinusoidal wave form - there is almost no advantage in microstepping with these motors since they practically "full step" anyway.
The spindle wiring with the Fwd/Rev switch was cumbersome. I replaced it with a standard drum switch from a manual mill. I will still wire it up with an E-Stop button and use a magnetic switch like this one:
The machine looks a lot more like a standard Bridgeport with both of the bulky cabinets removed.
After removing the unneeded parts, I cleaned the entire machine. To get the built-up grime removed, I "painted" on liberal amounts of Goop brand hand cleaner and let it soak for a while. It removed almost all the grime and even some oil stains that I thought were permanent. A word of caution though, the hand cleaner seems to soften the paint a little, so when I was rubbing off the grime, I noticed some gray paint on the rag also. The places that were well abraded by constant abuse from being battered by metal chips would remove paint along with the embedded chips.