Don't know about chip enclosure, probably if you can get the parts from Haas but it will be a big job.
Turret tool changer is field installable, I had it done. Actually I bought the machine with the original slow as molasses tool turret which was discontinued; then I seriously modified it rendering it unusable. The net result was I had to get the later model with the servo drive installed.
Tailstock can be just slid onto the guides assuming you can buy it loose from Haas.